Enzyme-containing foliar fertilizer for promoting yield increase of crops in the grouting period and preparation method thereof

Abstract

The application provides a kind of enzyme-containing leaf fertilizer for promoting yield increase of grouting period crop and a preparation method thereof, comprising: nitrogen fertilizer, phosphate fertilizer, potassium fertilizer, mixed bacteria powder and complex enzyme preparation are mixed to obtain a compound fertilizer, the mixed bacteria powder comprises Bacillus subtilis, Bacillus licheniformis, Bacillus mucilaginosus, Bacillus megaterium and lactic acid bacteria; The complex enzyme preparation comprises pectinase, cellulase and xylanase; The compound fertilizer is dispersed in a Tween 20 solution to obtain a fertilizer solution; The fertilizer solution is added to a cyclodextrin solution, and a coated modified compound fertilizer is obtained after freeze-drying; Chitosan, sodium alginate and deionized water are mixed to obtain a mixed solution; The coated modified compound fertilizer and the modified bentonite are added to obtain a composite sol; The composite sol is added dropwise into a calcium salt solution to obtain a hydrogel microbead precursor; The hydrogel microbead precursor is taken out and soaked in a sulfate solution to obtain a composite hydrogel microbead; And the enzyme-containing leaf fertilizer is obtained after freeze-drying of the composite hydrogel microbead.

Description

Technical Field

[0001] This invention belongs to the field of crop yield enhancement technology, and relates to an enzyme-containing foliar fertilizer that promotes crop yield enhancement during the grain-filling stage and its preparation method. Background Technology

[0002] The growth and development of crops can be broadly divided into three stages: the vegetative growth stage, the stage of simultaneous vegetative and reproductive growth, and the reproductive growth stage. In the third growth stage, after grain formation, the crop enters the grain-filling stage. The grain-filling stage refers to the period during which starch, protein, and accumulated organic matter produced through photosynthesis are assimilated and stored in the grain.

[0003] Insufficient fertilizer and water during the later stages of crop growth can cause premature aging of leaves and roots, and shorten the grain-filling period. Therefore, foliar fertilizer needs to be applied during the grain-filling stage to ensure yield. In addition, spraying foliar fertilizer can increase field humidity, which can help nourish leaves and protect grains, promote grain filling, increase grain weight, and improve quality.

[0004] Foliar fertilization involves spraying a nutrient solution that regulates plant growth and provides nutrients onto the leaves of plants. Foliar fertilizer cannot completely replace root fertilization; it can only supplement nutrients when soil fertility is insufficient or the plant roots are unable to absorb nutrients properly. For example, in the seedling stage when roots are underdeveloped, or in later stages of plant growth when root vitality decreases and nutrient absorption capacity weakens, or when soil conditions are unfavorable for root nutrient absorption. In these cases, foliar spraying can achieve twice the result with half the effort, quickly replenishing nutrients to meet the needs of crop growth and development. Foliar fertilization has become an important means of supplementing insufficient root fertilization and plays a crucial role in modern agriculture.

[0005] Currently, commonly used foliar fertilizers include urea, potassium dihydrogen phosphate, boron fertilizer, and all-element foliar fertilizers. However, commercially available foliar fertilizers generally suffer from serious losses, short-lasting effects, low utilization rates, and environmental pollution. Therefore, there is an urgent need to develop a new environmentally friendly, highly efficient, and slow-release foliar fertilizer. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide an enzyme-containing foliar fertilizer and its preparation method for promoting crop yield during the grain-filling stage. This invention employs a synergistic combination of enzymes and bacteria, using a blend of various specific functional strains and enzyme preparations, combined with nitrogen, phosphorus, and potassium fertilizers, to prepare a microecological compound foliar fertilizer. This fertilizer can effectively activate the activity of endogenous enzymes in crops, improve leaf photosynthetic efficiency, regulate nutrient transport and distribution, stimulate and regulate plant growth and development, enhance the leaves' ability to absorb and utilize soil nutrients, and strengthen the plant's metabolic function. This results in crops with high yield, low pollution, disease and pest resistance, and drought resistance, thereby achieving the effect of protecting leaves and increasing yield.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing an enzyme-containing foliar fertilizer that promotes crop yield increase during the grain-filling stage, the preparation method comprising:

[0009] (I) A compound fertilizer is obtained by mixing nitrogen fertilizer, phosphorus fertilizer, potassium fertilizer, compound bacterial powder and compound enzyme preparation, wherein the compound bacterial powder includes Bacillus subtilis, Bacillus licheniformis, Bacillus mucilaginosus, Bacillus megaterium and lactic acid bacteria; the compound enzyme preparation includes pectinase, cellulase and xylanase; the compound fertilizer is dispersed in Tween 20 solution and mixed evenly to obtain fertilizer solution;

[0010] (II) β-cyclodextrin is added to a silane coupling agent solution, mixed evenly, and then heated under reflux. The reaction product is filtered, washed, and dried to obtain amino-modified cyclodextrin. The amino-modified cyclodextrin is added to a polylactic acid solution, mixed, and then reacted to obtain grafted modified cyclodextrin. The grafted modified cyclodextrin is dispersed in N,N-dimethylformamide to obtain a cyclodextrin solution. The fertilizer solution is added to the cyclodextrin solution, mixed evenly, and then freeze-dried to obtain a coated modified compound fertilizer.

[0011] (III) Bentonite is added to a silane coupling agent solution, heated and stirred to react, and the reaction product is filtered, washed and dried to obtain amino-modified bentonite; hexadecyltrimethylammonium bromide, polycarboxylic acid metal chelating agent and aluminum hydroxide pillar agent are dispersed in deionized water and mixed evenly to obtain a composite modified solution; the amino-modified bentonite is dispersed in deionized water and mixed evenly to obtain a bentonite suspension, and the composite modified solution is added dropwise to the bentonite suspension, while stirring and heating are carried out continuously during the dropwise addition. After all the dropwise addition is completed, heating is continued for a period of time, and then the composite modified bentonite is obtained after filtration, washing and drying.

[0012] (IV) Chitosan, sodium alginate and deionized water are mixed and stirred evenly to obtain a mixture; the coated modified compound fertilizer and the modified bentonite are added to the mixture and ultrasonically dispersed to obtain a composite sol; the composite sol is added dropwise to a calcium salt solution and soaked for a period of time to obtain a hydrogel microbead precursor; the hydrogel microbead precursor is taken out and soaked in a sulfate solution to obtain composite hydrogel microbeads; the composite hydrogel microbeads are freeze-dried to obtain the enzyme-containing foliar fertilizer.

[0013] This invention employs a synergistic combination of enzymes and bacteria, blending various strains of bacteria with specific functions and enzyme preparations, along with nitrogen, phosphorus, and potassium fertilizers, to prepare a microecological compound foliar fertilizer. This compound fertilizer boasts comprehensive nutritional components, containing not only the macronutrients required by crops but also a variety of biological organic nutrients, providing a complete and balanced nutritional profile for crop growth. Using the foliar fertilizer prepared by this invention, crops are unaffected by soil factors. Utilizing the synergistic effect between enzymes and bacteria, various physiologically active substances and secondary metabolites are produced, effectively activating the activity of endogenous enzymes in crops, improving leaf photosynthetic efficiency, regulating nutrient transport and distribution, stimulating and regulating plant growth and development, enhancing the leaves' ability to absorb and utilize soil nutrients, and strengthening the plant's metabolic function. This results in crops with high yields, low pollution, disease and pest resistance, and drought resistance, thereby achieving the effect of protecting leaves and increasing yield.

[0014] The combined use of the compound enzyme preparation and compound microbial powder provided by this invention can effectively increase the protein content of crops, preserve more nutrients, and inhibit the growth and reproduction of harmful microorganisms. At the same time, it can also decompose insoluble nitrogen, phosphorus and potassium fertilizers into fast-acting nitrogen, phosphorus and potassium fertilizers that are more easily absorbed and utilized by crops, thereby improving the fertilizer efficiency and utilization rate of foliar fertilizers and playing a role in improving the quality and promoting the growth and development of crops.

[0015] Some microbial strains can also cause plant spoilage, reducing their nutritional and economic value, such as various putrefactive microorganisms; some strains can even make plants poisonous or spread diseases, causing poisoning or infectious diseases in consumers, such as some pathogens and fungi that cause plant mold. Therefore, the microbial strains used in the compound microbial powder directly determine the plant's production efficiency. This invention specifically screened five microbial strains: Bacillus subtilis, Bacillus licheniformis, Bacillus mucilage, Bacillus megaterium, and lactic acid bacteria, and compounded them in a specific ratio to obtain a compound microbial powder that combines safety and biological value.

[0016] Bacillus subtilis can promote plant growth, prevent soil-borne diseases, and thus achieve strong seedlings. It also has a good preventive effect on small leaves, yellow leaves, wilting, and stunted seedlings in crops.

[0017] Bacillus licheniformis can adjust the dysbiosis of the bacterial community on the surface of crop leaves to achieve therapeutic purposes. It can promote the production of antibacterial active substances in crop leaves and kill pathogens. In addition, Bacillus licheniformis also has a unique biological oxygen-scavenging mechanism, which can inhibit the growth and reproduction of pathogens.

[0018] Bacillus mucilaginosus can secrete crop growth stimulants and carbonic anhydrase to enhance crop resistance to diseases and promote carbon dioxide fixation. At the same time, it can also promote the conversion of ineffective phosphorus and potassium in compound fertilizers, increase the supply of effective phosphorus and potassium on the surface of crop leaves, and improve crop yield.

[0019] Bacillus megaterium is a microorganism with phosphorus-solubilizing and potassium-promoting functions. It can degrade organophosphates and aflatoxins and convert insoluble phosphorus and potassium into readily available phosphorus and potassium through its own metabolism. In the process of metabolism, it can also secrete metabolites such as indoleacetic acid and various organic acids that promote plant growth. In addition, Bacillus megaterium has a nitrogen-fixing synergistic effect when used in combination with Bacillus mucilaginosus.

[0020] During fermentation, lactic acid bacteria produce various organic acids such as lactic acid, acetic acid, citric acid, and phenyllactic acid. These organic acids lower the pH value and can combine with ions such as iron, aluminum, calcium, and magnesium, thereby dissolving insoluble phosphates. In addition, lactic acid bacteria also produce enzymatic reactions during phosphate solubilization, significantly increasing the activity of pectinase, cellulase, and xylanase.

[0021] Cellulase has the ability to efficiently degrade cellulose, breaking it down into oligosaccharides and monosaccharides. These oligosaccharides and monosaccharides can serve as carbon and energy sources for microbial growth and reproduction, promoting the growth of strains in compound microbial powders and enhancing the disease resistance of crops. Furthermore, cellulase can effectively remove the protein coating layer on the surface of fruits and vegetables, delaying water evaporation and spoilage, thereby effectively extending the shelf life of fruits and vegetables.

[0022] Pectinase is a type of enzyme that can break down the core of plant cell walls. When pectin is degraded by pectinase, the cell walls become fragile. Therefore, during fruit ripening, pectinase can promote the softening of the fruit skin, making it easier to peel and eat, and improving the fruit's texture. Furthermore, when pectinase is used in conjunction with cellulase, it can also disrupt the cell walls of oilseed crops, facilitating oil release and thus increasing the extraction rate of oilseeds.

[0023] Xylanase is a complex enzyme system that degrades hemicellulose xylan into water-soluble oligosaccharides and xylose. It can work in conjunction with cellulase to synergistically promote the growth of strains in compound bacterial powder, provide the necessary nutrients for strain growth, and promote the absorption and utilization of nutrients. In addition, xylanase can also promote the proliferation of probiotics and inhibit the growth of harmful bacteria.

[0024] This invention uses sodium alginate and chitosan as gel carriers, and achieves a staged slow-release function by combining them with β-cyclodextrin and bentonite. Composite hydrogel microbeads loaded with compound fertilizer are prepared by sol-gel method, and after freeze-drying, enzyme-containing foliar fertilizer is formed. The enzyme-containing foliar fertilizer prepared by this invention can produce different release rates and release effects at different stages of crop growth and development. In addition, the three-layer slow-release barrier of β-cyclodextrin, bentonite and composite gel system provides a relatively stable environment of temperature and humidity for the growth, reproduction and fermentation of enzymes in compound fertilizer.

[0025] The early stage of crop growth and development is the vegetative growth stage, during which soil fertilization is the main method and foliar fertilization is the supplementary method. Therefore, the release rate of foliar fertilizer should not be too high during this stage, otherwise it will lead to nutrient excess. The enzyme-containing foliar fertilizer prepared by this invention is mainly composed of a composite gel system in the early stage of fertilization. The composite gel system is structurally stable and does not easily absorb water. At the same time, there are three slow-release barriers in addition to the compound fertilizer: β-cyclodextrin, bentonite and gel system. At this time, it is difficult for the compound fertilizer to penetrate through these three slow-release barriers and seep into the external environment. Therefore, the release rate of the compound fertilizer is low at this time and can be carried out simultaneously with soil fertilization.

[0026] During the middle stage of crop growth and development, vegetative and reproductive growth occur simultaneously. Soil fertilization and foliar fertilization are carried out concurrently during this stage. The release rate of foliar fertilizer is at a moderate level during this stage. The enzyme-containing foliar fertilizer prepared in this invention is mainly based on the bentonite system during the middle stage of fertilization. At this time, the gel barrier decomposes due to prolonged water absorption, and the pore size on the gel surface gradually increases, thus losing its slow-release barrier function. At this time, the compound fertilizer is encapsulated and adsorbed by β-cyclodextrin into the bentonite layer. Therefore, there are two slow-release barriers, β-cyclodextrin and bentonite, in addition to the compound fertilizer. The compound fertilizer can then seep into the external environment by passing through the two slow-release barriers of β-cyclodextrin and bentonite. Therefore, the release rate of the compound fertilizer is at a moderate level at this time, and it gradually increases with the fertilization time.

[0027] The later stage of crop growth and development is the reproductive growth stage, during which foliar fertilization is the main method and soil fertilization is the supplementary method. The release rate of foliar fertilizer is relatively high during this stage. The enzyme-containing foliar fertilizer prepared by this invention is mainly composed of β-cyclodextrin system in the later stage of fertilization. At this time, as the enzyme-containing foliar fertilizer continues to absorb water and swell, the coated modified compound fertilizer is separated from the interlayer of boron nitride, and boron nitride also loses its slow-release barrier function. At this time, the compound fertilizer is only encapsulated by β-cyclodextrin. The compound fertilizer can seep into the external environment by passing through the slow-release barrier of β-cyclodextrin. Therefore, the release rate of compound fertilizer reaches the highest level at this time.

[0028] This invention uses hexadecyltrimethylammonium bromide, polycarboxylated metal chelating agents, and aluminum hydroxide pillar agents as multi-component composite modifiers to perform organic-inorganic composite modification treatment on bentonite. There is a synergistic intercalation effect among the multi-component composite modifiers, which is conducive to the simultaneous entry of different types of intercalation modifiers into the interlayer of bentonite, thereby effectively increasing the interlayer spacing of bentonite.

[0029] On the one hand, polycarboxylic acid metal chelating agents are relatively small in size and have more negatively charged branches. They can be sandwiched in the larger positively charged long carbon chain hexadecyltrimethylammonium bromide and polyhydroxyaluminum ions through electrostatic interaction, so that the multi-component composite modifier can be inserted into the interlayer domain of bentonite at the same time, thereby increasing its interlayer spacing.

[0030] On the other hand, both hexadecyltrimethylammonium bromide and polyhydroxyaluminum ions are positively charged, while polycarboxylic acid metal chelators contain multiple carboxyl functional groups. Under certain conditions, they dissociate to form negatively charged carboxylate ions. The negatively charged anions can act as a link to bridge the positively charged hexadecyltrimethylammonium bromide and polyhydroxyaluminum ions together through electrostatic forces. The bridged hexadecyltrimethylammonium bromide and polyhydroxyaluminum ions can enter the interlayer of bentonite as a whole, thereby further increasing the interlayer spacing of the composite modified bentonite.

[0031] On the other hand, polycarboxylic acid metal chelating agents contain multiple carboxyl functional groups, while aluminum hydroxide pillar agents contain multiple hydroxyl functional groups. A large number of hydrogen bonds are easily formed between polycarboxylic acid metal chelating agents and polyaluminum hydroxide ions. As an intermolecular force that plays an auxiliary role, hydrogen bonds can further promote the synergistic insertion of multi-component composite modifiers into the interlayer of bentonite, thereby achieving the purpose of multi-component modification.

[0032] The modified composite bentonite of this invention combines the excellent properties of both pillared bentonite and organic bentonite. The aluminum hydroxyl pillar agent, which enters the interlayer, occupies some of the exchangeable ion sites. The positively charged aluminum hydroxyl pillar agent is stably maintained by electrostatic attraction and the excess negative charge between the bentonite layers, aligning along a direction perpendicular to the crystal layers. This expands the interlayer spacing of the bentonite, thereby increasing the adsorption capacity of the composite modified bentonite for coated modified compound fertilizers. This improves the adsorption performance of the composite modified bentonite, enabling it to accommodate more coated modified compound fertilizers. Simultaneously, after organic modification with hexadecyltrimethylammonium bromide, the hexadecyltrimethylammonium bromide and aluminum hydroxyl ions adsorbed between the composite modified bentonite layers exceed the cation exchange capacity of the bentonite. Therefore, the final composite modified bentonite carries a certain positive charge, which, under the effect of charge repulsion, significantly improves its dispersion performance in the composite sol.

[0033] This invention uses sodium alginate and chitosan as carriers for a composite gel system, resulting in a dense three-dimensional porous network structure within the prepared composite hydrogel microspheres. Due to the strong hydrophilicity of sodium alginate, the final composite hydrogel microspheres have a high water content, allowing the formation of large ice crystals during freeze-drying. The ice crystals within the composite hydrogel microspheres sublimate, and air replaces the ice crystals, preserving the original three-dimensional macroporous network structure of the composite hydrogel. This interconnected macroporous structure is beneficial for the dissolution and release of compound fertilizers.

[0034] This invention adds chitosan to sodium alginate, utilizing the electrostatic interaction between sodium alginate and chitosan to increase the cross-linking density of the hydrogel. This results in a denser three-dimensional porous network structure of the composite hydrogel microspheres, extending the release channels of the compound fertilizer within the microspheres and thus hindering its release and penetration, achieving a slow-release effect. Furthermore, the dense three-dimensional porous network structure significantly improves the mechanical strength compared to sodium alginate gel alone. This is because during the ionic cross-linking of sodium alginate and chitosan, both molecules possess numerous functional groups for reaction, leading to a more complete reaction and a greater number of opposite charges. This results in a denser cross-linked network, enhancing the mechanical properties of the composite hydrogel microspheres.

[0035] Sodium alginate exhibits instantaneous gelation upon contact with calcium ions, forming a hydrogel network. Chitosan, on the other hand, can crosslink with sulfate ions to form a stable gel network. Furthermore, the primary amino groups on the chitosan molecular chain and the carboxyl groups on the sodium alginate molecular chain can undergo a polyelectrolyte complexation reaction under electrostatic forces to form composite hydrogel microspheres. The composite hydrogel microspheres prepared through dual crosslinking with calcium and sulfate ions have a more stable structure and are less prone to disintegration, providing favorable conditions for the slow release of the compound fertilizer within them.

[0036] As a preferred technical solution of the present invention, in step (I), the compound fertilizer comprises the following components in parts by weight:

[0037] 30-40 parts nitrogen fertilizer;

[0038] 20-30 parts phosphate fertilizer;

[0039] 20-30 parts potassium fertilizer;

[0040] 5-10 parts of compound bacterial powder;

[0041] 3-8 portions of compound enzyme preparation.

[0042] The nitrogen fertilizer can be in the following weight proportions: 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 parts; the phosphate fertilizer can be in the following weight proportions: 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 parts; the potassium fertilizer can be in the following weight proportions: 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 parts; compound fertilizer... The weight parts of the bacterial powder can be 5.0 parts, 5.5 parts, 6.0 parts, 6.5 parts, 7.0 parts, 7.5 parts, 8.0 parts, 8.5 parts, 9.0 parts, 9.5 parts, or 10.0 parts; the weight parts of the compound enzyme preparation can be 3.0 parts, 3.5 parts, 4.0 parts, 4.5 parts, 5.0 parts, 5.5 parts, 6.0 parts, 6.5 parts, 7.0 parts, 7.5 parts, or 8.0 parts, but are not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] As a preferred technical solution of the present invention, in step (I), the nitrogen fertilizer includes any one or a combination of at least two of urea, ammonium sulfate or ammonium nitrate.

[0044] In some alternative examples, the phosphate fertilizer includes any one or a combination of at least two of superphosphate, monoammonium phosphate, or diammonium phosphate.

[0045] In some alternative examples, the potassium fertilizer includes any one or a combination of at least two of potassium sulfate, potassium nitrate, potassium carbonate, or potassium chloride.

[0046] In some optional examples, the mass ratio of Bacillus subtilis, Bacillus licheniformis, Bacillus mucilaginosus, Bacillus megaterium, and lactic acid bacteria in the compound bacterial powder is (1~1.5):(0.8~1.2):(0.6~0.9):(0.5~0.7):(1~1.2), for example, it can be 1:0.8:0.6:0.5:1, 1.1:0.9:0.7:0.55:1, 1.2:1:0.8:0.6:1, 1.3:1.1:0.8:0.65:1.1, or 1.5:1.2:0.9:0.7:1.2, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0047] In some optional examples, the mass ratio of pectinase, cellulase and xylanase in the compound enzyme preparation is (2~2.5):(1~1.5):(2.5~3), for example, it can be 2:1:2.5, 2.1:1.1:2.6, 2.2:1.2:2.7, 2.3:1.3:2.8, 2.4:1.4:2.9 or 2.5:1.5:3, but is not limited to the values ​​listed, other unlisted values ​​within this range are also applicable.

[0048] In some optional examples, the surfactant comprises any one or a combination of at least two of sodium hexyl sulfate, sodium octyl sulfonate, sodium dodecyl sulfate, or EO / PO block polyether.

[0049] In some optional instances, the mass fraction of compound fertilizer in the fertilizer solution is 20 to 30 wt%, for example, it can be 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, or 30 wt%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0050] As a preferred technical solution of the present invention, in step (II), the silane coupling agent solution is composed of silane coupling agent and ethanol aqueous solution.

[0051] In some optional instances, the mass fraction of the silane coupling agent in the silane coupling agent solution is 10 to 20 wt%, for example, it can be 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, or 20 wt%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0052] In some alternative instances, the mass ratio of the β-cyclodextrin to the silane coupling agent in the silane coupling agent solution is 1:(0.1~0.5), for example, it can be 1:0.1, 1:0.15, 1:0.2, 1:0.25, 1:0.3, 1:0.35, 1:0.4, 1:0.45 or 1:0.5, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0053] In some alternative instances, the temperature of the heating reflux reaction is 50 to 60°C, for example, 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C or 60°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0054] In some alternative instances, the heating reflux reaction time is 3 to 4 hours, for example, 3.0 hours, 3.1 hours, 3.2 hours, 3.3 hours, 3.4 hours, 3.5 hours, 3.6 hours, 3.7 hours, 3.8 hours, 3.9 hours, or 4.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0055] As a preferred technical solution of the present invention, in step (II), the mass fraction of polylactic acid in the polylactic acid solution is 5~15wt%, for example, it can be 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt% or 15wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0056] In some alternative examples, the mass ratio of the aminocyclodextrin to the polylactic acid in the polylactic acid solution is (10~15):1, for example, it can be 10.0:1, 10.5:1, 11.0:1, 11.5:1, 12.0:1, 12.5:1, 13.0:1, 13.5:1, 14.0:1, 14.5:1 or 15.0:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0057] In some alternative examples, the temperature for mixing the aminocyclodextrin with the polylactic acid solution is 70-80°C, for example, 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C or 80°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0058] In some alternative examples, the reaction time of the aminocyclodextrin with the polylactic acid solution is 5 to 8 hours, for example, 5.0 hours, 5.2 hours, 5.4 hours, 5.6 hours, 5.8 hours, 6.0 hours, 6.2 hours, 6.4 hours, 6.6 hours, 6.8 hours, 7.0 hours, 7.2 hours, 7.4 hours, 7.6 hours, 7.8 hours, or 8.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0059] In some optional instances, the mass fraction of grafted modified cyclodextrin in the cyclodextrin solution is 5 to 10 wt%, for example, it can be 5.0 wt%, 5.5 wt%, 6.0 wt%, 6.5 wt%, 7.0 wt%, 7.5 wt%, 8.0 wt%, 8.5 wt%, 9.0 wt%, 9.5 wt%, or 10.0 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0060] In some optional instances, the mass ratio of the compound fertilizer in the fertilizer solution to the grafted modified cyclodextrin in the cyclodextrin solution is 1:(10~20), for example, it can be 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19 or 1:20, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0061] This invention achieves a phased slow-release effect of foliar fertilizer through a three-layer slow-release barrier formed by β-cyclodextrin, boron nitride, and composite gel. In the three stages of crop growth and development, the inclusion effect of grafted modified cyclodextrin has a significant impact on the dissolution rate of compound fertilizer in the reproductive growth stage.

[0062] When the amount of grafted modified cyclodextrin added is below the lower limit of the range defined in this invention, the grafted modified cyclodextrin fails to completely encapsulate the compound fertilizer, resulting in a high dissolution rate of the compound fertilizer. As the amount of grafted modified cyclodextrin added gradually increases, the grafted modified cyclodextrin can completely encapsulate the compound fertilizer, and the slow-release control effect of the grafted modified cyclodextrin is fully utilized, further reducing the dissolution rate of the compound fertilizer. In addition, because the surface of the grafted modified cyclodextrin contains a large number of hydroxyl groups, it has the characteristics of being hydrophilic on the outside and hydrophobic on the inside. Introducing grafted modified cyclodextrin into the composite gel system can increase the water absorption of the composite hydrogel microspheres, improve the hydrophilicity of the foliar fertilizer, and increase the swelling degree of the foliar fertilizer. When the amount of grafted modified cyclodextrin added exceeds the upper limit of the range defined in this invention, it will lead to an increase in the cross-linking density of the composite gel system, and the grafted modified cyclodextrin will be more dense in the gel system, resulting in an increase in intermolecular hydrogen bonds and a decrease in the swelling degree of the foliar fertilizer.

[0063] In some alternative instances, the freeze-drying temperature is -30 to -20°C, for example, -30°C, -29°C, -28°C, -27°C, -26°C, -25°C, -24°C, -23°C, -22°C, -21°C, or -20°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0064] In some optional instances, the freeze-drying time is 1 to 3 hours, for example, 1.0 hours, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2.0 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, or 3.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0065] As a preferred technical solution of the present invention, in step (III), the silane coupling agent solution is composed of silane coupling agent and ethanol aqueous solution.

[0066] In some optional instances, the mass fraction of the silane coupling agent in the silane coupling agent solution is 10 to 20 wt%, for example, it can be 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, or 20 wt%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0067] In some alternative examples, the mass ratio of the bentonite to the silane coupling agent in the silane coupling agent solution is 1:(1.2~1.3), for example, it can be 1:1.2, 1:1.21, 1:1.22, 1:1.23, 1:1.24, 1:1.25, 1:1.26, 1:1.27, 1:1.28, 1:1.29 or 1:1.3, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0068] In some alternative examples, the reaction temperature of the bentonite with the silane coupling agent solution is 100~110°C, for example, 100°C, 101°C, 102°C, 103°C, 104°C, 105°C, 106°C, 107°C, 108°C, 109°C or 110°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0069] In some alternative examples, the reaction time of the bentonite with the silane coupling agent solution is 0.5 to 1.5 h, for example, 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1.0 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h or 1.5 h, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0070] As a preferred technical solution of the present invention, in step (III), the concentration of hexadecyltrimethylammonium bromide in the composite modified solution is 0.1~0.25 mol / L, for example, it can be 0.1 mol / L, 0.11 mol / L, 0.12 mol / L, 0.13 mol / L, 0.14 mol / L, 0.15 mol / L, 0.16 mol / L, 0.17 mol / L, 0.18 mol / L, 0.19 mol / L, 0.2 mol / L, 0.21 mol / L, 0.22 mol / L, 0.23 mol / L, 0.24 mol / L or 0.25 mol / L, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0071] In some optional instances, the mass ratio of the hexadecyltrimethylammonium bromide to the amino-modified bentonite in the bentonite suspension is (0.2-0.3):1, for example, it can be 0.2:1, 0.21:1, 0.22:1, 0.23:1, 0.24:1, 0.25:1, 0.26:1, 0.27:1, 0.28:1, 0.29:1 or 0.3:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0072] The amount of hexadecyltrimethylammonium bromide added significantly affects the release rate of compound fertilizer. As the amount of hexadecyltrimethylammonium bromide added increases, the release rate of the compound fertilizer gradually decreases and tends to stabilize. When the mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite is in the range of (0.2-0.3):1, hexadecyltrimethylammonium bromide is adsorbed into the interlayer of bentonite via ion exchange. Its cation end combines with the negatively charged centers on the bentonite surface through electrostatic interaction, while its long carbon chains aggregate to form an organic phase. The compound fertilizer enters the interlayer organic phase of bentonite through partitioning. When the concentration of the compound fertilizer in the planting environment is lower than its equilibrium concentration, the compound fertilizer dissolves and leaches out under the action of the concentration gradient. Simultaneously, the slow-release effect is achieved by the hindrance of the long carbon chains of hexadecyltrimethylammonium bromide.

[0073] When the mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite is less than 0.2:1, the interlayer spacing of the bentonite is too small, preventing the compound fertilizer from effectively entering the interlayer organic phase of the bentonite. Consequently, the inhibitory effect on the release of the compound fertilizer is not significant, and the staged slow-release effect of cyclodextrin-bentonite-composite gel cannot be achieved. Increasing the amount of hexadecyltrimethylammonium bromide can improve the interlayer spacing of the bentonite, thereby increasing the interfacial area between the interlayer organic phase and the aqueous phase, which is beneficial for the release of the compound fertilizer. Furthermore, it can enhance the inhibitory effect on the diffusion of compound fertilizer molecules, thus slowing down its release rate.

[0074] When the mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite exceeds 0.3:1, further increasing the amount of hexadecyltrimethylammonium bromide added does not significantly increase the interlayer spacing of the organic bentonite. This is because the amount of hexadecyltrimethylammonium bromide added is too high, exceeding the total amount of exchangeable cations. Excess hexadecyltrimethylammonium bromide is adsorbed into the interlayer domain of bentonite through hydrophobic interactions, competing with the adsorption of compound fertilizer. At the same time, since there is no stable binding between excess hexadecyltrimethylammonium bromide and bentonite, it will move and diffuse in the interlayer domain of bentonite and even be released into the environment, thus having a very limited inhibitory effect on the diffusion of compound fertilizer.

[0075] In some optional examples, the ratio of the polycarboxylated metal chelating agent to the amino-modified bentonite in the bentonite suspension is (0.3~0.8) mL:1g, for example, it can be 0.3mL:1g, 0.35mL:1g, 0.4mL:1g, 0.45mL:1g, 0.5mL:1g, 0.55mL:1g, 0.5mL:1g, 0.6mL:1g, 0.65mL:1g, 0.7mL:1g, 0.75mL:1g or 0.8mL:1g, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0076] In some optional examples, the polycarboxylated metal chelating agent includes any one or a combination of at least two of tetraethylenepentamine, triethylenetetramine, ethylenediamine, or diethylenetriamine.

[0077] In some optional examples, the ratio of the amount of aluminum ions in the aluminum hydroxyl pillar to the amino-modified bentonite in the bentonite suspension is (1.0~1.5) mmol:1g, for example, it can be 1.0 mmol:1g, 1.05 mmol:1g, 1.1 mmol:1g, 1.15 mmol:1g, 1.2 mmol:1g, 1.25 mmol:1g, 1.3 mmol:1g, 1.35 mmol:1g, 1.4 mmol:1g, 1.45 mmol:1g or 1.5 mmol:1g, but is not limited to the values ​​listed, other unlisted values ​​within this range are also applicable.

[0078] In some optional instances, the mass fraction of amino-modified bentonite in the bentonite suspension is 1-5 wt%, for example, it may be 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 3.5 wt%, 4.0 wt%, 4.5 wt%, or 5.0 wt%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0079] In some alternative instances, the heating temperature is 50-60°C, for example, 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C or 60°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0080] In some optional instances, after all the composite modified solution has been added dropwise, the heating continues for 1 to 2 hours, for example, 1.0 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h, or 2.0 h, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0081] As a preferred technical solution of the present invention, in step (IV), the concentration of chitosan in the mixture is 10~20 mg / mL, for example, it can be 10 mg / mL, 11 mg / mL, 12 mg / mL, 13 mg / mL, 14 mg / mL, 15 mg / mL, 16 mg / mL, 17 mg / mL, 18 mg / mL, 19 mg / mL or 20 mg / mL, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0082] In some optional examples, the mass ratio of the chitosan, the sodium alginate, the coated modified compound fertilizer, and the modified bentonite is (2~3):(0.4~0.5):10:(0.5~0.6), for example, it can be 2:0.4:10:0.5, 2.1:0.41:10:0.51, 2.2:0.42:10:0.52, 2.3:0.43:10:0.53, etc. 2.4:0.44:10:0.54, 2.5:0.45:10:0.55, 2.6:0.46:10:0.56, 2.7:0.47:10:0.57, 2.8:0.48:10:0.58, 2.9:0.49:10:0.59, or 3:0.5:10:0.6, but not limited to the listed values; other unlisted values ​​within this range also apply.

[0083] The foliar fertilizer exhibits maximum swelling when the amount of sodium alginate added is within the range specified in this invention. When the amount of sodium alginate added is below the lower limit specified in this invention, the number of active reaction sites is insufficient, resulting in poor cross-linking of the generated polymer. Consequently, the composite hydrogel microspheres cannot form a dense surface, and water cannot be retained within the three-dimensional porous network structure of the composite hydrogel microspheres for an extended period. This leads to a decrease in the swelling degree and poor water retention of the final foliar fertilizer. When the amount of sodium alginate added exceeds the upper limit specified in this invention, the sodium alginate content in the gel system is too high, causing the sodium alginate molecular chains to entangle into clumps. During the gelation process, the graft copolymerization reaction can only occur on the surface of the clump-like sodium alginate, while the reaction is difficult to occur inside the clump-like sodium alginate. This reduces the effective active reaction sites and grafting rate, further decreasing the swelling degree and water retention of the foliar fertilizer.

[0084] In some optional instances, the ultrasonic dispersion uses an ultrasonic power of 80 to 100 kW, such as 80 kW, 82 kW, 84 kW, 86 kW, 88 kW, 90 kW, 92 kW, 94 kW, 96 kW, 98 kW or 100 kW, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0085] In some optional instances, the ultrasonic dispersion treatment time is 1 to 3 hours, for example, 1.0 hours, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2.0 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, or 3.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0086] As a preferred technical solution of the present invention, in step (IV), the dropping rate of the composite sol is 0.1~0.2 mL / s, for example, it can be 0.1 mL / s, 0.11 mL / s, 0.12 mL / s, 0.13 mL / s, 0.14 mL / s, 0.15 mL / s, 0.16 mL / s, 0.17 mL / s, 0.18 mL / s, 0.19 mL / s or 0.2 mL / s, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0087] In some optional instances, the mass fraction of the calcium salt solution is 2 to 3 wt%, for example, it may be 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, 2.9 wt%, or 3.0 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0088] This invention specifically limits the mass fraction of the calcium salt solution to 2-3 wt%. Within this range, the foliar fertilizer exhibits the greatest swelling degree. As the mass fraction of the calcium salt solution increases, the swelling degree of the foliar fertilizer decreases. This is because when the mass fraction of the calcium salt solution is below 2 wt%, the degree of ionic cross-linking on the surface of the composite hydrogel microspheres is low, resulting in a loose and porous structure. Water entering the interior of the composite hydrogel microspheres will then seep out again through the pores on the surface. Therefore, water cannot be stored inside the composite hydrogel microspheres for a long time, leading to low swelling degree and poor water retention. When the mass fraction of the calcium salt solution exceeds 2 wt%, the ionic cross-linking on the surface of the composite hydrogel microspheres is more dense, making it difficult for water to penetrate the surface and enter the interior of the composite hydrogel microspheres, resulting in low swelling degree and poor water absorption.

[0089] In some optional instances, the immersion time of the droplets of the composite sol in the calcium salt solution is 10 to 20 minutes, for example, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes or 20 minutes, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0090] In some alternative examples, the sulfate solution has a mass fraction of 2 to 3 wt%, for example, 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, 2.9 wt%, or 3.0 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0091] In some optional instances, the immersion time of the hydrogel microbead precursor in the sulfate solution is 10-20 min, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min or 20 min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0092] In some optional instances, the freeze-drying temperature of the composite hydrogel microspheres is -40 to -20°C, for example, -40°C, -38°C, -36°C, -34°C, -32°C, -30°C, -28°C, -26°C, -24°C, -22°C, or -20°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0093] In some optional examples, the freeze-drying time of the composite hydrogel microspheres is 6 to 12 hours, for example, 6.0 hours, 6.5 hours, 7.0 hours, 7.5 hours, 8.0 hours, 8.5 hours, 9.0 hours, 9.5 hours, 10.0 hours, 10.5 hours, 11.0 hours, 11.5 hours, or 12.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0094] For example, the present invention provides a method for preparing an enzyme-containing foliar fertilizer that promotes crop yield increase during the grain-filling stage, the preparation method comprising:

[0095] (1) Mix 30-40 parts of nitrogen fertilizer, 20-30 parts of phosphate fertilizer, 20-30 parts of potassium fertilizer, 5-10 parts of compound microbial powder and 3-8 parts of compound enzyme preparation to obtain compound fertilizer; wherein, the compound microbial powder includes Bacillus subtilis, Bacillus licheniformis, Bacillus mucilaginosus, Bacillus megaterium and lactic acid bacteria in a mass ratio of (1-1.5):(0.8-1.2):(0.6-0.9):(0.5-0.7):(1-1.2), and the compound enzyme preparation includes pectinase, cellulase and xylanase in a mass ratio of (2-2.5):(1-1.5):(2.5-3); disperse the compound fertilizer in Tween 20 solution, mix evenly to obtain a fertilizer solution of 20-30 wt%;

[0096] (2) Add β-cyclodextrin to a 10-20 wt% silane coupling agent solution, the mass ratio of β-cyclodextrin to silane coupling agent is 1:(0.1-0.5), mix evenly and then heat under reflux for 50-60℃ for 3-4 h. The reaction product is filtered, washed and dried to obtain amino-modified cyclodextrin. Add amino-modified cyclodextrin to a 5-15 wt% polylactic acid solution, the mass ratio of amino-modified cyclodextrin to polylactic acid is (10-15):1, mix and react at 70-80℃ for 5-8 h to obtain grafted modified cyclodextrin.

[0097] Grafted modified cyclodextrin was dispersed in N,N-dimethylformamide to obtain a 5-10 wt% cyclodextrin solution. Fertilizer solution was added to the cyclodextrin solution. The mass ratio of compound fertilizer to grafted modified cyclodextrin was 1:(10-20). After mixing evenly, the mixture was freeze-dried at -30~-20℃ for 1-3 hours to obtain the coated modified compound fertilizer.

[0098] (3) Add bentonite to a 10-20 wt% silane coupling agent solution, with a mass ratio of bentonite to silane coupling agent of 1:(1.2-1.3). Heat and stir at 100-110℃ for 0.5-1.5 h to allow the reaction to occur. The reaction product is filtered, washed and dried to obtain amino-modified bentonite.

[0099] Hexadecyltrimethylammonium bromide, a polycarboxylic acid metal chelating agent, and an aluminum hydroxide pillaring agent were dispersed in deionized water and mixed thoroughly to obtain a composite modified solution. The concentration of hexadecyltrimethylammonium bromide in the composite modified solution was 0.1~0.25 mol / L. Amino-modified bentonite was dispersed in deionized water and mixed thoroughly to obtain a bentonite suspension with a mass fraction of 1-5 wt%. The composite modified solution was added dropwise to the bentonite suspension. The concentration of hexadecyltrimethylammonium bromide and the amino-modified bentonite were mixed thoroughly. The mass ratio of the modified bentonite to the amino-modified bentonite was (0.2-0.3):1, the ratio of the polycarboxylated metal chelating agent to the amino-modified bentonite was (0.3-0.8) mL:1g, and the ratio of the amount of aluminum ions in the aluminum hydroxide pillar agent to the amino-modified bentonite was (1.0-1.5) mmol:1g. During the dropwise addition, the mixture was continuously stirred and heated in a water bath at 50-60℃. After all the addition was completed, the water bath heating was maintained for 1-2 hours. Then, the mixture was filtered, washed, and dried to obtain the composite modified bentonite.

[0100] (4) Chitosan, sodium alginate and deionized water are mixed and stirred to obtain a mixture. The concentration of chitosan in the mixture is 10~20mg / mL. The coated modified compound fertilizer obtained in step (2) and the composite modified bentonite obtained in step (3) are added to the mixture. The mass ratio of chitosan, sodium alginate, coated modified compound fertilizer and composite modified bentonite is (2~3):(0.4~0.5):10:(0.5~0.6). After mixing evenly, the mixture is ultrasonically dispersed at 80~100kW for 1~3h to obtain a composite sol.

[0101] The composite sol was added dropwise to a 2-3 wt% calcium salt solution at a dropping rate of 0.1-0.2 mL / s and soaked for 10-20 min to obtain a hydrogel microbead precursor. The hydrogel microbead precursor was then removed and soaked in a 2-3 wt% sulfate solution for 10-20 min to obtain composite hydrogel microbeads. The composite hydrogel microbeads were freeze-dried at -40 to -20℃ for 6-12 h to obtain the enzyme-containing foliar fertilizer.

[0102] Secondly, the present invention provides an enzyme-containing foliar fertilizer for promoting crop yield increase during the grain-filling stage, prepared by the preparation method described in the first aspect.

[0103] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0104] This invention employs a synergistic combination of enzymes and bacteria, blending various strains of bacteria with specific functions and enzyme preparations, along with nitrogen, phosphorus, and potassium fertilizers, to prepare a microecological compound foliar fertilizer. This compound fertilizer boasts comprehensive nutritional components, containing not only the macronutrients required by crops but also a variety of biological organic nutrients, providing a complete and balanced nutritional profile for crop growth. Using the foliar fertilizer prepared by this invention, crops are unaffected by soil factors. Utilizing the synergistic effect between enzymes and bacteria, various physiologically active substances and secondary metabolites are produced, effectively activating the activity of endogenous enzymes in crops, improving leaf photosynthetic efficiency, regulating nutrient transport and distribution, stimulating and regulating plant growth and development, enhancing the leaves' ability to absorb and utilize soil nutrients, and strengthening the plant's metabolic function. This results in crops with high yields, low pollution, disease and pest resistance, and drought resistance, thereby achieving the effect of protecting leaves and increasing yield.

[0105] The combined use of the compound enzyme preparation and compound microbial powder provided by this invention can effectively increase the protein content of crops, preserve more nutrients, and inhibit the growth and reproduction of harmful microorganisms. At the same time, it can also decompose insoluble nitrogen, phosphorus and potassium fertilizers into fast-acting nitrogen, phosphorus and potassium fertilizers that are more easily absorbed and utilized by crops, thereby improving the fertilizer efficiency and utilization rate of foliar fertilizers and playing a role in improving the quality and promoting the growth and development of crops.

[0106] Some microbial strains can also cause plant spoilage, reducing their nutritional and economic value, such as various putrefactive microorganisms; some strains can even make plants poisonous or spread diseases, causing poisoning or infectious diseases in consumers, such as some pathogens and fungi that cause plant mold. Therefore, the microbial strains used in the compound microbial powder directly determine the plant's production efficiency. This invention specifically screened five microbial strains: Bacillus subtilis, Bacillus licheniformis, Bacillus mucilage, Bacillus megaterium, and lactic acid bacteria, and compounded them in a specific ratio to obtain a compound microbial powder that combines safety and biological value.

[0107] Bacillus subtilis can promote plant growth, prevent soil-borne diseases, and thus achieve strong seedlings. It also has a good preventive effect on small leaves, yellow leaves, wilting, and stunted seedlings in crops.

[0108] Bacillus licheniformis can adjust the dysbiosis of the bacterial community on the surface of crop leaves to achieve therapeutic purposes. It can promote the production of antibacterial active substances in crop leaves and kill pathogens. In addition, Bacillus licheniformis also has a unique biological oxygen-scavenging mechanism, which can inhibit the growth and reproduction of pathogens.

[0109] Bacillus mucilaginosus can secrete crop growth stimulants and carbonic anhydrase to enhance crop resistance to diseases and promote carbon dioxide fixation. At the same time, it can also promote the conversion of ineffective phosphorus and potassium in compound fertilizers, increase the supply of effective phosphorus and potassium on the surface of crop leaves, and improve crop yield.

[0110] Bacillus megaterium is a microorganism with phosphorus-solubilizing and potassium-promoting functions. It can degrade organophosphates and aflatoxins and convert insoluble phosphorus and potassium into readily available phosphorus and potassium through its own metabolism. In the process of metabolism, it can also secrete metabolites such as indoleacetic acid and various organic acids that promote plant growth. In addition, Bacillus megaterium has a nitrogen-fixing synergistic effect when used in combination with Bacillus mucilaginosus.

[0111] During fermentation, lactic acid bacteria produce various organic acids such as lactic acid, acetic acid, citric acid, and phenyllactic acid. These organic acids lower the pH value and can combine with ions such as iron, aluminum, calcium, and magnesium, thereby dissolving insoluble phosphates. In addition, lactic acid bacteria also produce enzymatic reactions during phosphate solubilization, significantly increasing the activity of pectinase, cellulase, and xylanase.

[0112] Cellulase has the ability to efficiently degrade cellulose, breaking it down into oligosaccharides and monosaccharides. These oligosaccharides and monosaccharides can serve as carbon and energy sources for microbial growth and reproduction, promoting the growth of strains in compound microbial powders and enhancing the disease resistance of crops. Furthermore, cellulase can effectively remove the protein coating layer on the surface of fruits and vegetables, delaying water evaporation and spoilage, thereby effectively extending the shelf life of fruits and vegetables.

[0113] Pectinase is a type of enzyme that can break down the core of plant cell walls. When pectin is degraded by pectinase, the cell walls become fragile. Therefore, during fruit ripening, pectinase can promote the softening of the fruit skin, making it easier to peel and eat, and improving the fruit's texture. Furthermore, when pectinase is used in conjunction with cellulase, it can also disrupt the cell walls of oilseed crops, facilitating oil release and thus increasing the extraction rate of oilseeds.

[0114] Xylanase is a complex enzyme system that degrades hemicellulose xylan into water-soluble oligosaccharides and xylose. It can work in conjunction with cellulase to synergistically promote the growth of strains in compound bacterial powder, provide the necessary nutrients for strain growth, and promote the absorption and utilization of nutrients. In addition, xylanase can also promote the proliferation of probiotics and inhibit the growth of harmful bacteria.

[0115] This invention uses sodium alginate and chitosan as gel carriers, and achieves a staged slow-release function by combining them with β-cyclodextrin and bentonite. Composite hydrogel microbeads loaded with compound fertilizer are prepared by sol-gel method, and after freeze-drying, enzyme-containing foliar fertilizer is formed. The enzyme-containing foliar fertilizer prepared by this invention can produce different release rates and release effects at different stages of crop growth and development. In addition, the three-layer slow-release barrier of β-cyclodextrin, bentonite and composite gel system provides a relatively stable environment of temperature and humidity for the growth, reproduction and fermentation of enzymes in compound fertilizer.

[0116] The early stage of crop growth and development is the vegetative growth stage, during which soil fertilization is the main method and foliar fertilization is the supplementary method. Therefore, the release rate of foliar fertilizer should not be too high during this stage, otherwise it will lead to nutrient excess. The enzyme-containing foliar fertilizer prepared by this invention is mainly composed of a composite gel system in the early stage of fertilization. The composite gel system is structurally stable and does not easily absorb water. At the same time, there are three slow-release barriers in addition to the compound fertilizer: β-cyclodextrin, bentonite and gel system. At this time, it is difficult for the compound fertilizer to penetrate through these three slow-release barriers and seep into the external environment. Therefore, the release rate of the compound fertilizer is low at this time and can be carried out simultaneously with soil fertilization.

[0117] During the middle stage of crop growth and development, vegetative and reproductive growth occur simultaneously. Soil fertilization and foliar fertilization are carried out concurrently during this stage. The release rate of foliar fertilizer is at a moderate level during this stage. The enzyme-containing foliar fertilizer prepared in this invention is mainly based on the bentonite system during the middle stage of fertilization. At this time, the gel barrier decomposes due to prolonged water absorption, and the pore size on the gel surface gradually increases, thus losing its slow-release barrier function. At this time, the compound fertilizer is encapsulated and adsorbed by β-cyclodextrin into the bentonite layer. Therefore, there are two slow-release barriers, β-cyclodextrin and bentonite, in addition to the compound fertilizer. The compound fertilizer can then seep into the external environment by passing through the two slow-release barriers of β-cyclodextrin and bentonite. Therefore, the release rate of the compound fertilizer is at a moderate level at this time, and it gradually increases with the fertilization time.

[0118] The later stage of crop growth and development is the reproductive growth stage, during which foliar fertilization is the main method and soil fertilization is the supplementary method. The release rate of foliar fertilizer is relatively high during this stage. The enzyme-containing foliar fertilizer prepared by this invention is mainly composed of β-cyclodextrin system in the later stage of fertilization. At this time, as the enzyme-containing foliar fertilizer continues to absorb water and swell, the coated modified compound fertilizer is separated from the interlayer of boron nitride, and boron nitride also loses its slow-release barrier function. At this time, the compound fertilizer is only encapsulated by β-cyclodextrin. The compound fertilizer can seep into the external environment by passing through the slow-release barrier of β-cyclodextrin. Therefore, the release rate of compound fertilizer reaches the highest level at this time.

[0119] This invention uses hexadecyltrimethylammonium bromide, polycarboxylated metal chelating agents, and aluminum hydroxide pillar agents as multi-component composite modifiers to perform organic-inorganic composite modification treatment on bentonite. There is a synergistic intercalation effect among the multi-component composite modifiers, which is conducive to the simultaneous entry of different types of intercalation modifiers into the interlayer of bentonite, thereby effectively increasing the interlayer spacing of bentonite.

[0120] On the one hand, polycarboxylic acid metal chelating agents are relatively small in size and have more negatively charged branches. They can be sandwiched in the larger positively charged long carbon chain hexadecyltrimethylammonium bromide and polyhydroxyaluminum ions through electrostatic interaction, so that the multi-component composite modifier can be inserted into the interlayer domain of bentonite at the same time, thereby increasing its interlayer spacing.

[0121] On the other hand, both hexadecyltrimethylammonium bromide and polyhydroxyaluminum ions are positively charged, while polycarboxylic acid metal chelators contain multiple carboxyl functional groups. Under certain conditions, they dissociate to form negatively charged carboxylate ions. The negatively charged anions can act as a link to bridge the positively charged hexadecyltrimethylammonium bromide and polyhydroxyaluminum ions together through electrostatic forces. The bridged hexadecyltrimethylammonium bromide and polyhydroxyaluminum ions can enter the interlayer of bentonite as a whole, thereby further increasing the interlayer spacing of the composite modified bentonite.

[0122] On the other hand, polycarboxylic acid metal chelating agents contain multiple carboxyl functional groups, while aluminum hydroxide pillar agents contain multiple hydroxyl functional groups. A large number of hydrogen bonds are easily formed between polycarboxylic acid metal chelating agents and polyaluminum hydroxide ions. As an intermolecular force that plays an auxiliary role, hydrogen bonds can further promote the synergistic insertion of multi-component composite modifiers into the interlayer of bentonite, thereby achieving the purpose of multi-component modification.

[0123] The modified composite bentonite of this invention combines the excellent properties of both pillared bentonite and organic bentonite. The aluminum hydroxyl pillar agent, which enters the interlayer, occupies some of the exchangeable ion sites. The positively charged aluminum hydroxyl pillar agent is stably maintained by electrostatic attraction and the excess negative charge between the bentonite layers, aligning along a direction perpendicular to the crystal layers. This expands the interlayer spacing of the bentonite, thereby increasing the adsorption capacity of the composite modified bentonite for coated modified compound fertilizers. This improves the adsorption performance of the composite modified bentonite, enabling it to accommodate more coated modified compound fertilizers. Simultaneously, after organic modification with hexadecyltrimethylammonium bromide, the hexadecyltrimethylammonium bromide and aluminum hydroxyl ions adsorbed between the composite modified bentonite layers exceed the cation exchange capacity of the bentonite. Therefore, the final composite modified bentonite carries a certain positive charge, which, under the effect of charge repulsion, significantly improves its dispersion performance in the composite sol.

[0124] This invention uses sodium alginate and chitosan as carriers for a composite gel system, resulting in a dense three-dimensional porous network structure within the prepared composite hydrogel microspheres. Due to the strong hydrophilicity of sodium alginate, the final composite hydrogel microspheres have a high water content, allowing the formation of large ice crystals during freeze-drying. The ice crystals within the composite hydrogel microspheres sublimate, and air replaces the ice crystals, preserving the original three-dimensional macroporous network structure of the composite hydrogel. This interconnected macroporous structure is beneficial for the dissolution and release of compound fertilizers.

[0125] This invention adds chitosan to sodium alginate, utilizing the electrostatic interaction between sodium alginate and chitosan to increase the cross-linking density of the hydrogel. This results in a denser three-dimensional porous network structure of the composite hydrogel microspheres, extending the release channels of the compound fertilizer within the microspheres and thus hindering its release and penetration, achieving a slow-release effect. Furthermore, the dense three-dimensional porous network structure significantly improves the mechanical strength compared to sodium alginate gel alone. This is because during the ionic cross-linking of sodium alginate and chitosan, both molecules possess numerous functional groups for reaction, leading to a more complete reaction and a greater number of opposite charges. This results in a denser cross-linked network, enhancing the mechanical properties of the composite hydrogel microspheres.

[0126] Sodium alginate exhibits instantaneous gelation upon contact with calcium ions, forming a hydrogel network. Chitosan, on the other hand, can crosslink with sulfate ions to form a stable gel network. Furthermore, the primary amino groups on the chitosan molecular chain and the carboxyl groups on the sodium alginate molecular chain can undergo a polyelectrolyte complexation reaction under electrostatic forces to form composite hydrogel microspheres. The composite hydrogel microspheres prepared through dual crosslinking with calcium and sulfate ions have a more stable structure and are less prone to disintegration, providing favorable conditions for the slow release of the compound fertilizer within them. Attached Figure Description

[0127] Figure 1 The process flow diagrams for preparing enzyme-containing foliar fertilizers provided in Examples 1-11 of this invention are shown below.

[0128] Figure 2 Infrared spectra of unmodified bentonite and the composite modified bentonite prepared in Example 1 of this invention;

[0129] Figure 3 XRD patterns of unmodified bentonite and composite modified bentonite prepared in Example 1 of this invention;

[0130] Figure 4 This is a scanning electron microscope image of the surface of the enzyme-containing foliar fertilizer prepared in Example 1 of the present invention;

[0131] Figure 5 This is a scanning electron microscope image of the surface of the enzyme-containing foliar fertilizer prepared in Example 1 of the present invention;

[0132] Figure 6 This is a cross-sectional scanning electron microscope image of the enzyme-containing foliar fertilizer prepared in Example 1 of the present invention;

[0133] Figure 7 This is a cross-sectional scanning electron microscope image of the enzyme-containing foliar fertilizer prepared in Example 1 of the present invention. Detailed Implementation

[0134] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be construed as limiting the implementation methods or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0135] Example 1

[0136] This embodiment provides a method for preparing an enzyme-containing foliar fertilizer that promotes crop yield increase during the grain-filling stage, such as... Figure 1 As shown, the preparation method includes:

[0137] (1) Mix 30 parts of urea, 20 parts of superphosphate, 20 parts of potassium sulfate, 5 parts of compound bacterial powder and 3 parts of compound enzyme preparation to obtain compound fertilizer; wherein, the compound bacterial powder includes Bacillus subtilis, Bacillus licheniformis, Bacillus mucilaginosus, Bacillus megaterium and lactic acid bacteria in a mass ratio of 1:0.8:0.6:0.5:1, and the compound enzyme preparation includes pectinase, cellulase and xylanase in a mass ratio of 2:1:2.5; disperse the compound fertilizer in Tween 20 solution (Tween 20 mass fraction is 20wt%), mix evenly to obtain 20wt% fertilizer solution;

[0138] (2) β-cyclodextrin was added to a 10wt% solution of silane coupling agent KH550, with a mass ratio of β-cyclodextrin to silane coupling agent KH550 of 1:0.1. After mixing evenly, the mixture was heated under reflux at a temperature of 50℃ for 4 hours. The reaction product was filtered, washed and dried to obtain amino-modified cyclodextrin. Amino-modified cyclodextrin was added to a 5wt% solution of polylactic acid, with a mass ratio of amino-modified cyclodextrin to polylactic acid of 10:1. After mixing and reacting at 70℃ for 8 hours, grafted modified cyclodextrin was obtained.

[0139] Grafted modified cyclodextrin was dispersed in N,N-dimethylformamide to obtain a 5wt% cyclodextrin solution. Fertilizer solution was added to the cyclodextrin solution. The mass ratio of compound fertilizer to grafted modified cyclodextrin was 1:10. After mixing evenly, the mixture was freeze-dried at -30℃ for 1 hour to obtain the coated modified compound fertilizer.

[0140] (3) Add bentonite to a 10wt% solution of silane coupling agent KH550. The mass ratio of bentonite to silane coupling agent KH550 is 1:1.2. Heat and stir at 100℃ for 1.5h to react. The reaction product is filtered, washed and dried to obtain amino-modified bentonite.

[0141] Hexadecyltrimethylammonium bromide, tetraethylenepentamine, and aluminum hydroxyl pillar agent were dispersed in deionized water and mixed evenly to obtain a composite modified solution, wherein the concentration of hexadecyltrimethylammonium bromide in the composite modified solution was 0.1 mol / L. Amino-modified bentonite was dispersed in deionized water and mixed evenly to obtain a bentonite suspension with a mass fraction of 1 wt%. The composite modified solution was added dropwise to the bentonite suspension, wherein the mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite was 0.2:1, the ratio of tetraethylenepentamine to amino-modified bentonite was 0.3 mL:1 g, and the molar amount of aluminum ions in the aluminum hydroxyl pillar agent to amino-modified bentonite was 1 mmol:1 g. During the dropwise addition, the mixture was continuously stirred and heated in a water bath at 50°C. After all the addition was completed, the water bath heating was maintained for 1 hour. Subsequently, the mixture was filtered, washed, and dried to obtain the composite modified bentonite.

[0142] (4) Chitosan, sodium alginate and deionized water are mixed and stirred to obtain a mixture with a chitosan concentration of 10 mg / mL. The coated modified compound fertilizer obtained in step (2) and the composite modified bentonite obtained in step (3) are added to the mixture. The mass ratio of chitosan, sodium alginate, coated modified compound fertilizer and composite modified bentonite is 2:0.4:10:0.5. After mixing evenly, the mixture is ultrasonically dispersed at 80 kW for 3 h to obtain a composite sol.

[0143] The composite sol was added dropwise to a 2 wt% calcium chloride solution at a rate of 0.1 mL / s and soaked for 10 min to obtain a hydrogel microbead precursor. The hydrogel microbead precursor was then removed and soaked in a 2 wt% sodium sulfate solution for 10 min to obtain composite hydrogel microbeads. The composite hydrogel microbeads were freeze-dried at -40℃ for 6 h to obtain the enzyme-containing foliar fertilizer.

[0144] Infrared spectroscopy analysis was performed on unmodified bentonite and the composite modified bentonite prepared in this embodiment, and the results were as follows: Figure 2 The infrared spectrum shown is from Figure 2 It can be seen that 1723cm -1 A new absorption peak appeared at 2851 cm⁻¹, which is attributed to the characteristic absorption peak of the Al-O stretching vibration in the aluminum hydroxyl pillar, indicating that aluminum hydroxyl ions have entered the interlayer of bentonite. Furthermore, at 2851 cm⁻¹... -1 and 2920cm -1 Two new absorption peaks appeared at 1474 cm⁻¹, attributed to the characteristic absorption peaks of the symmetric and antisymmetric stretching vibrations of HCH in the -CH₂ functional group of hexadecyltrimethylammonium bromide. Additionally, at 1474 cm⁻¹... -1 A new absorption peak appeared, which is attributed to the bending vibration absorption peak of the carboxyl group of tetraethylenepentamine, indicating that both CTAB and the metal chelating agent successfully entered the interlayer of bentonite.

[0145] X-ray diffraction (XRD) was used to perform XRD tests on unmodified bentonite and the composite modified bentonite prepared in this embodiment. The XRD tube was a Cu target, the voltage was set to 40 kV, the current to 30 mA, the scan rate to 1.5 / min, the scan range to 5-60°, and the scan wavelength to 0.15 nm. The XRD results are as follows: Figure 3 The XRD patterns shown are used to calculate the interlayer spacing of unmodified bentonite and composite modified bentonite. The calculated interlayer spacing of unmodified bentonite is 1.252 nm, while that of composite modified bentonite is 2.188 nm. This indicates that the interlayer spacing of bentonite is significantly improved after multi-component composite modification.

[0146] Figure 4 and Figure 5 This is a scanning electron microscope (SEM) image of the surface of the enzyme-containing foliar fertilizer prepared in this embodiment. Figure 4 and Figure 5 It can be seen that the enzyme-containing foliar fertilizer has a spherical shape and a smooth and dense surface, which plays a key role in inhibiting the release of compound fertilizer. Figure 6 and Figure 7 This is a cross-sectional scanning electron microscope image of the enzyme-containing foliar fertilizer prepared in this embodiment. Figure 6 and Figure 7 It can be seen that it has a rich three-dimensional porous network structure with an average pore size of 100μm, which can effectively prevent the diffusion and dissolution of compound fertilizer inside it.

[0147] Example 2

[0148] This embodiment provides a method for preparing an enzyme-containing foliar fertilizer that promotes crop yield increase during the grain-filling stage, such as... Figure 1 As shown, the preparation method includes:

[0149] (1) A compound fertilizer is obtained by mixing 32 parts of ammonium sulfate, 22 parts of monoammonium phosphate, 22 parts of potassium nitrate, 6 parts of compound bacterial powder and 4 parts of compound enzyme preparation; wherein, the compound bacterial powder includes Bacillus subtilis, Bacillus licheniformis, Bacillus mucilaginosus, Bacillus megaterium and lactic acid bacteria in a mass ratio of 1.2:0.9:0.75:0.6:1.1, and the compound enzyme preparation includes pectinase, cellulase and xylanase in a mass ratio of 2.2:1.2:2.7; the compound fertilizer is dispersed in Tween 20 solution (Tween 20 mass fraction is 20wt%), and mixed evenly to obtain a 22wt% fertilizer solution;

[0150] (2) β-cyclodextrin was added to a 12wt% solution of silane coupling agent KH550, with a mass ratio of β-cyclodextrin to silane coupling agent KH550 of 1:0.2. After mixing evenly, the mixture was heated under reflux at a temperature of 52℃ for 3.8h. The reaction product was filtered, washed and dried to obtain amino-modified cyclodextrin. Amino-modified cyclodextrin was added to an 8wt% solution of polylactic acid, with a mass ratio of amino-modified cyclodextrin to polylactic acid of 11:1. After mixing and reacting at 72℃ for 7h, grafted modified cyclodextrin was obtained.

[0151] Grafted modified cyclodextrin was dispersed in N,N-dimethylformamide to obtain a 6wt% cyclodextrin solution. Fertilizer solution was added to the cyclodextrin solution. The mass ratio of compound fertilizer to grafted modified cyclodextrin was 1:12. After mixing evenly, the mixture was freeze-dried at -28℃ for 1.5h to obtain the coated modified compound fertilizer.

[0152] (3) Add bentonite to a 12wt% solution of silane coupling agent KH550. The mass ratio of bentonite to silane coupling agent KH550 is 1:1.22. Heat and stir at 102℃ for 1.2h to react. The reaction product is filtered, washed and dried to obtain amino-modified bentonite.

[0153] Hexadecyltrimethylammonium bromide, triethylenetetramine, and aluminum hydroxide pillaring agent were dispersed in deionized water and mixed thoroughly to obtain a composite modified solution. The concentration of hexadecyltrimethylammonium bromide in the composite modified solution was 0.15 mol / L. Amino-modified bentonite was dispersed in deionized water and mixed thoroughly to obtain a bentonite suspension with a mass fraction of 2 wt%. The composite modified solution was added dropwise to the bentonite suspension. The mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite was 0.22:1, the ratio of triethylenetetramine to amino-modified bentonite was 0.4 mL:1 g, and the molar amount of aluminum ions in the aluminum hydroxide pillaring agent to amino-modified bentonite was 1.1 mmol:1 g. During the dropwise addition, the mixture was continuously stirred and heated in a water bath at 52 °C. After all the addition was completed, the water bath heating was maintained for 1.2 h. Subsequently, the mixture was filtered, washed, and dried to obtain the composite modified bentonite.

[0154] (4) Chitosan, sodium alginate and deionized water are mixed and stirred to obtain a mixture with a chitosan concentration of 12 mg / mL. The coated modified compound fertilizer obtained in step (2) and the composite modified bentonite obtained in step (3) are added to the mixture. The mass ratio of chitosan, sodium alginate, coated modified compound fertilizer and composite modified bentonite is 2.2:0.42:10:0.52. After mixing evenly, the mixture is ultrasonically dispersed at 85 kW for 2.5 h to obtain a composite sol.

[0155] The composite sol was added dropwise to a 2.2 wt% calcium chloride solution at a rate of 0.12 mL / s and soaked for 12 min to obtain a hydrogel microbead precursor. The hydrogel microbead precursor was then removed and soaked in a 2.2 wt% sodium sulfate solution for 12 min to obtain composite hydrogel microbeads. The composite hydrogel microbeads were freeze-dried at -35℃ for 8 h to obtain the enzyme-containing foliar fertilizer.

[0156] Example 3

[0157] This embodiment provides a method for preparing an enzyme-containing foliar fertilizer that promotes crop yield increase during the grain-filling stage, such as... Figure 1 As shown, the preparation method includes:

[0158] (1) A compound fertilizer is obtained by mixing 35 parts of ammonium nitrate, 25 parts of diammonium phosphate, 25 parts of potassium carbonate, 7 parts of compound bacterial powder and 5 parts of compound enzyme preparation; wherein, the compound bacterial powder includes Bacillus subtilis, Bacillus licheniformis, Bacillus mucilaginosus, Bacillus megaterium and lactic acid bacteria in a mass ratio of 1.3:1:0.8:0.65:1.15, and the compound enzyme preparation includes pectinase, cellulase and xylanase in a mass ratio of 2.3:1.3:2.8; the compound fertilizer is dispersed in Tween 20 solution (Tween 20 mass fraction is 20wt%), and mixed evenly to obtain a 25wt% fertilizer solution;

[0159] (2) β-cyclodextrin was added to a 15wt% solution of silane coupling agent KH560, with a mass ratio of β-cyclodextrin to silane coupling agent KH560 of 1:0.3. After mixing evenly, the mixture was heated under reflux at a temperature of 55℃ for 3.5h. The reaction product was filtered, washed and dried to obtain amino-modified cyclodextrin. Amino-modified cyclodextrin was added to a 10wt% solution of polylactic acid, with a mass ratio of amino-modified cyclodextrin to polylactic acid of 12:1. After mixing and reacting at 75℃ for 6h, grafted modified cyclodextrin was obtained.

[0160] Grafted modified cyclodextrin was dispersed in N,N-dimethylformamide to obtain a 7wt% cyclodextrin solution. Fertilizer solution was added to the cyclodextrin solution. The mass ratio of compound fertilizer to grafted modified cyclodextrin was 1:15. After mixing evenly, the mixture was freeze-dried at -25℃ for 2 hours to obtain the coated modified compound fertilizer.

[0161] (3) Add bentonite to a 15wt% solution of silane coupling agent KH560. The mass ratio of bentonite to silane coupling agent KH560 is 1:1.25. Heat and stir at 105℃ for 1h to react. The reaction product is filtered, washed and dried to obtain amino-modified bentonite.

[0162] Hexadecyltrimethylammonium bromide, ethylenediamine, and aluminum hydroxide pillaring agent were dispersed in deionized water and mixed thoroughly to obtain a composite modified solution. The concentration of hexadecyltrimethylammonium bromide in the composite modified solution was 0.2 mol / L. Amino-modified bentonite was dispersed in deionized water and mixed thoroughly to obtain a bentonite suspension with a mass fraction of 3 wt%. The composite modified solution was added dropwise to the bentonite suspension. The mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite was 0.25:1, the ratio of ethylenediamine to amino-modified bentonite was 0.5 mL:1 g, and the molar ratio of aluminum ions in the aluminum hydroxide pillaring agent to amino-modified bentonite was 1.2 mmol:1 g. During the dropwise addition, the mixture was continuously stirred and heated in a water bath at 55 °C. After all the addition was completed, the water bath heating was maintained for 1.5 h. Subsequently, the mixture was filtered, washed, and dried to obtain the composite modified bentonite.

[0163] (4) Chitosan, sodium alginate and deionized water are mixed and stirred to obtain a mixture with a chitosan concentration of 15 mg / mL. The coated modified compound fertilizer obtained in step (2) and the composite modified bentonite obtained in step (3) are added to the mixture. The mass ratio of chitosan, sodium alginate, coated modified compound fertilizer and composite modified bentonite is 2.5:0.45:10:0.55. After mixing evenly, the mixture is ultrasonically dispersed at 90 kW for 2 h to obtain a composite sol.

[0164] The composite sol was added dropwise to a 2.5 wt% calcium chloride solution at a rate of 0.15 mL / s and soaked for 15 min to obtain a hydrogel microbead precursor. The hydrogel microbead precursor was then removed and soaked in a 2.5 wt% sodium sulfate solution for 15 min to obtain composite hydrogel microbeads. The composite hydrogel microbeads were freeze-dried at -30℃ for 10 h to obtain the enzyme-containing foliar fertilizer.

[0165] Example 4

[0166] This embodiment provides a method for preparing an enzyme-containing foliar fertilizer that promotes crop yield increase during the grain-filling stage, such as... Figure 1 As shown, the preparation method includes:

[0167] (1) A compound fertilizer was obtained by mixing 38 parts of urea, 28 parts of superphosphate, 28 parts of potassium chloride, 8 parts of compound bacterial powder and 6 parts of compound enzyme preparation; wherein, the compound bacterial powder included Bacillus subtilis, Bacillus licheniformis, Bacillus mucilaginosus, Bacillus megaterium and lactic acid bacteria in a mass ratio of 1.4:1.1:0.8:0.65:1.1, and the compound enzyme preparation included pectinase, cellulase and xylanase in a mass ratio of 2.4:1.4:2.9; the compound fertilizer was dispersed in Tween 20 solution (Tween 20 mass fraction is 20wt%), and mixed evenly to obtain a 28wt% fertilizer solution;

[0168] (2) β-cyclodextrin was added to a 18wt% solution of silane coupling agent KH560, with a mass ratio of β-cyclodextrin to silane coupling agent KH560 of 1:0.4. After mixing evenly, the mixture was heated under reflux at a temperature of 58℃ for 3.2h. The reaction product was filtered, washed and dried to obtain amino-modified cyclodextrin. Amino-modified cyclodextrin was added to a 12wt% solution of polylactic acid, with a mass ratio of amino-modified cyclodextrin to polylactic acid of 13:1. After mixing and reacting at 78℃ for 6h, grafted modified cyclodextrin was obtained.

[0169] Grafted modified cyclodextrin was dispersed in N,N-dimethylformamide to obtain an 8wt% cyclodextrin solution. Fertilizer solution was added to the cyclodextrin solution. The mass ratio of compound fertilizer to grafted modified cyclodextrin was 1:18. After mixing evenly, the mixture was freeze-dried at -22℃ for 2.5h to obtain the coated modified compound fertilizer.

[0170] (3) Add bentonite to a 18wt% solution of silane coupling agent KH560. The mass ratio of bentonite to silane coupling agent KH560 is 1:1.28. Heat and stir at 108℃ for 0.8h to react. The reaction product is filtered, washed and dried to obtain amino-modified bentonite.

[0171] Hexadecyltrimethylammonium bromide, diethylenetriamine, and aluminum hydroxide pillaring agent were dispersed in deionized water and mixed thoroughly to obtain a composite modified solution. The concentration of hexadecyltrimethylammonium bromide in the composite modified solution was 0.2 mol / L. Amino-modified bentonite was dispersed in deionized water and mixed thoroughly to obtain a bentonite suspension with a mass fraction of 4 wt%. The composite modified solution was added dropwise to the bentonite suspension. The mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite was 0.28:1, the ratio of diethylenetriamine to amino-modified bentonite was 0.6 mL:1 g, and the molar amount of aluminum ions in the aluminum hydroxide pillaring agent to amino-modified bentonite was 1.3 mmol:1 g. During the dropwise addition, the mixture was continuously stirred and heated in a water bath at 58 °C. After all the addition was completed, the water bath heating was maintained for 1.8 h. Subsequently, the mixture was filtered, washed, and dried to obtain the composite modified bentonite.

[0172] (4) Chitosan, sodium alginate and deionized water are mixed and stirred to obtain a mixture. The concentration of chitosan in the mixture is 18 mg / mL. The coated modified compound fertilizer obtained in step (2) and the composite modified bentonite obtained in step (3) are added to the mixture. The mass ratio of chitosan, sodium alginate, coated modified compound fertilizer and composite modified bentonite is 2.8:0.48:10:0.58. After mixing evenly, the mixture is ultrasonically dispersed at 95 kW for 1.5 h to obtain a composite sol.

[0173] The composite sol was added dropwise to a 2.8 wt% calcium chloride solution at a rate of 0.18 mL / s and soaked for 18 min to obtain a hydrogel microbead precursor. The hydrogel microbead precursor was then removed and soaked in a 2.8 wt% sodium sulfate solution for 18 min to obtain composite hydrogel microbeads. The composite hydrogel microbeads were freeze-dried at -25℃ for 11 h to obtain the enzyme-containing foliar fertilizer.

[0174] Example 5

[0175] This embodiment provides a method for preparing an enzyme-containing foliar fertilizer that promotes crop yield increase during the grain-filling stage, such as... Figure 1 As shown, the preparation method includes:

[0176] (1) Mix 40 parts of urea, 30 parts of monoammonium phosphate, 30 parts of potassium nitrate, 10 parts of compound bacterial powder and 8 parts of compound enzyme preparation to obtain compound fertilizer; wherein, the compound bacterial powder includes Bacillus subtilis, Bacillus licheniformis, Bacillus mucilaginosus, Bacillus megaterium and lactic acid bacteria in a mass ratio of 1.5:1.2:0.9:0.7:1.2, and the compound enzyme preparation includes pectinase, cellulase and xylanase in a mass ratio of 2.5:1.5:3; disperse the compound fertilizer in Tween 20 solution (Tween 20 mass fraction is 20wt%) and mix evenly to obtain a 30wt% fertilizer solution;

[0177] (2) β-cyclodextrin was added to a 20wt% solution of silane coupling agent KH570, with a mass ratio of β-cyclodextrin to silane coupling agent KH570 of 1:0.5. After mixing evenly, the mixture was heated under reflux at a temperature of 60℃ for 3 hours. The reaction product was filtered, washed and dried to obtain amino-modified cyclodextrin. Amino-modified cyclodextrin was added to a 15wt% solution of polylactic acid, with a mass ratio of amino-modified cyclodextrin to polylactic acid of 15:1. After mixing and reacting at 80℃ for 5 hours, grafted modified cyclodextrin was obtained.

[0178] Grafted modified cyclodextrin was dispersed in N,N-dimethylformamide to obtain a 10wt% cyclodextrin solution. Fertilizer solution was added to the cyclodextrin solution. The mass ratio of compound fertilizer to grafted modified cyclodextrin was 1:20. After mixing evenly, the mixture was freeze-dried at -20℃ for 3 hours to obtain the coated modified compound fertilizer.

[0179] (3) Add bentonite to a 20wt% solution of silane coupling agent KH570. The mass ratio of bentonite to silane coupling agent KH570 is 1:1.3. Heat and stir at 110℃ for 0.5h to react. The reaction product is filtered, washed and dried to obtain amino-modified bentonite.

[0180] Hexadecyltrimethylammonium bromide, diethylenetriamine, and aluminum hydroxide pillaring agent were dispersed in deionized water and mixed thoroughly to obtain a composite modified solution. The concentration of hexadecyltrimethylammonium bromide in the composite modified solution was 0.25 mol / L. Amino-modified bentonite was dispersed in deionized water and mixed thoroughly to obtain a bentonite suspension with a mass fraction of 5 wt%. The composite modified solution was added dropwise to the bentonite suspension. The mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite was 0.3:1, the ratio of diethylenetriamine to amino-modified bentonite was 0.8 mL:1 g, and the molar ratio of aluminum ions in the aluminum hydroxide pillaring agent to amino-modified bentonite was 1.5 mmol:1 g. During the dropwise addition, the mixture was continuously stirred and heated in a water bath at 60 °C. After all the addition was completed, the water bath heating was maintained for 2 hours. The resulting product was then filtered, washed, and dried to obtain the composite modified bentonite.

[0181] (4) Chitosan, sodium alginate and deionized water are mixed and stirred to obtain a mixture with a chitosan concentration of 20 mg / mL. The coated modified compound fertilizer obtained in step (2) and the composite modified bentonite obtained in step (3) are added to the mixture. The mass ratio of chitosan, sodium alginate, coated modified compound fertilizer and composite modified bentonite is 3:0.5:10:0.6. After mixing evenly, the mixture is ultrasonically dispersed at 100 kW for 1 h to obtain a composite sol.

[0182] The composite sol was added dropwise to a 3 wt% calcium chloride solution at a rate of 0.2 mL / s and soaked for 20 min to obtain a hydrogel microbead precursor. The hydrogel microbead precursor was then removed and soaked in a 3 wt% sodium sulfate solution for 20 min to obtain composite hydrogel microbeads. The composite hydrogel microbeads were freeze-dried at -20℃ for 12 h to obtain the enzyme-containing foliar fertilizer.

[0183] Example 6

[0184] This embodiment provides a method for preparing an enzyme-containing foliar fertilizer that promotes crop yield increase during the grain-filling stage. The difference from Embodiment 1 is that in step (2), the mass ratio of compound fertilizer to grafted modified cyclodextrin is adjusted to 1:8, while other process parameters and operation steps are exactly the same as in Embodiment 1.

[0185] Example 7

[0186] This embodiment provides a method for preparing an enzyme-containing foliar fertilizer that promotes crop yield increase during the grain-filling stage. The difference from Embodiment 1 is that in step (2), the mass ratio of compound fertilizer to grafted modified cyclodextrin is adjusted to 1:23, while other process parameters and operation steps are exactly the same as in Embodiment 1.

[0187] Example 8

[0188] This embodiment provides a method for preparing an enzyme-containing foliar fertilizer that promotes crop yield increase during the grain-filling stage. The difference from Example 1 is that in step (3), the mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite is adjusted to 0.1:1, while other process parameters and operating steps are exactly the same as in Example 1.

[0189] Example 9

[0190] This embodiment provides a method for preparing an enzyme-containing foliar fertilizer that promotes crop yield increase during the grain-filling stage. The difference from Embodiment 1 is that in step (3), the mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite is adjusted to 0.4:1. Other process parameters and operating steps are exactly the same as in Embodiment 1.

[0191] Example 10

[0192] This embodiment provides a method for preparing an enzyme-containing foliar fertilizer that promotes crop yield increase during the grain-filling stage. The difference from Embodiment 1 is that in step (4), the mass ratio of chitosan, sodium alginate, coated modified compound fertilizer and compound modified bentonite is adjusted to 2:0.3:10:0.5. Other process parameters and operation steps are exactly the same as in Embodiment 1.

[0193] Example 11

[0194] This embodiment provides a method for preparing an enzyme-containing foliar fertilizer that promotes crop yield increase during the grain-filling stage. The difference from Embodiment 1 is that in step (4), the mass ratio of chitosan, sodium alginate, coated modified compound fertilizer and compound modified bentonite is adjusted to 2:0.6:10:0.5. Other process parameters and operation steps are exactly the same as in Embodiment 1.

[0195] Application examples

[0196] The enzyme-containing foliar fertilizer prepared in Example 1 of this invention was used in the potato planting process. The specific operation steps are as follows:

[0197] An experimental area was set up with a planting area of ​​200m². 2 Prepare raised beds on level ground, with a row spacing of 70-80cm, and plant in single rows with a plant spacing of 15-18cm. Cover with 10-13cm of soil, maintaining 4000-4500 seedlings per mu (approximately 667 square meters). Prepare a 500-fold dilution (concentration 2.0 × 10⁻⁶) using the enzyme-containing foliar fertilizer obtained in Example 1 above. 5 (cfu / mL, hereinafter referred to as this product), apply as a foliar spray once on the 30th, 45th and 60th day after the potatoes emerge, with a spraying amount of 40mL / acre each time;

[0198] Control area 1 was set up with a planting area of ​​200m².2 Prepare raised beds on level ground, with a row spacing of 70-80cm. Plant in single rows with a plant spacing of 15-18cm. Cover with 10-13cm of soil, maintaining 4000-4500 seedlings per mu (approximately 667 square meters). Prepare a 500-fold dilution (2.0 × 10⁻⁶) of commercially available Stanley controlled-release fertilizer. 5 (cfu / mL, hereinafter referred to as commercially available product), apply as a foliar spray once each on the 30th, 45th and 60th day after the potatoes emerge, with a spraying amount of 40mL / acre each time;

[0199] Control area 2 was set up with a planting area of ​​200m². 2 Prepare raised beds on flat ground with a row spacing of 70-80cm. Plant in single rows with a plant spacing of 15-18cm. Cover the plants with 10-13cm of soil and maintain 4000-4500 seedlings per mu. Apply foliar spray with clean water on the 30th, 45th, and 60th days after the potatoes emerge, with each application being 40mL / mu.

[0200] The results showed that, compared with control area 2, the symptoms of leaf wrinkling and dwarfing were partially alleviated after spraying the commercially available product in control area 1, and the average yield per mu increased by 13.5%. Compared with control area 2, the symptoms of leaf wrinkling and dwarfing were significantly alleviated after spraying the product in the experimental area, and the average yield per mu increased by 28.2%. After spraying the product, potatoes grew well, had a low incidence of pests and diseases, and high foliar fertilizer utilization, which helped to enhance photosynthesis, improve potato yield and quality, and had good economic benefits and market promotion value.

[0201] The swelling rate, water retention rate, and slow-release performance of the enzyme-containing foliar fertilizers prepared in Examples 1-11 were tested. The specific test steps are as follows:

[0202] (1) Swelling rate

[0203] A certain mass of sample was placed in an 80℃ oven and vacuum dried for 1 hour. The dried sample was weighed and recorded as M2 (g). At room temperature, the dried sample was completely immersed in deionized water for 48 hours to allow it to fully swell. The swollen sample was then removed, and the surface moisture was blotted dry with filter paper. The swollen sample was weighed and recorded as M1 (g). The swelling rate (SR, %) of the sample was calculated using the following formula:

[0204] .

[0205] (2) Water retention rate

[0206] A certain mass of sample was placed in an 80℃ oven for vacuum drying for 1 hour. The dried sample was then completely immersed in deionized water for 48 hours to reach swelling equilibrium at room temperature. The swollen sample was weighed and recorded as W (g). It was then placed in a constant temperature and humidity environment of 25°C and 30% for 12 hours, and then weighed again and recorded as W. p (g) The water retention rate (WH, %) of the sample is calculated using the following formula:

[0207] .

[0208] (3) Sustained-release performance

[0209] According to the requirements of standard GB / T23348-2009 "Standard for Slow-Release Fertilizers", the cumulative release rate of the enzyme-containing foliar fertilizers prepared in Examples 1-11 was tested in still water at 25℃ on the 15th and 30th days.

[0210] The test results are shown in Table 1.

[0211] Table 1

[0212] Swelling rate % Water retention rate % 15-day cumulative release rate % 30-day cumulative release rate % Example 1 82.1 87.6 60.6 82.7 Example 2 84.3 90.5 58.2 80.3 Example 3 88.7 91.4 56.4 77.5 Example 4 90.2 92.7 52.5 75.1 Example 5 93.4 95.2 50.1 70.8 Example 6 67.8 72.3 85.7 93.6 Example 7 70.6 75.9 82.5 91.8 Example 8 72.5 78.2 80.0 90.3 Example 9 74.9 81.0 76.3 86.4 Example 10 52.3 67.6 90.2 97.0 Example 11 58.0 70.1 87.2 95.2

[0213] As can be seen from the test data of Examples 1-5, the enzyme-containing foliar fertilizer prepared by the present invention has excellent water retention and slow-release capabilities. It can produce different release rates and effects at different stages of crop growth and development, which is conducive to improving the utilization rate of compound fertilizers and also meets the concept of green and sustainable development. It has broad application prospects in actual production.

[0214] The test data from Examples 1, 6, and 7 show that the swelling rate and water retention rate of the enzyme-containing foliar fertilizers prepared in Examples 6 and 7 are lower than those in Example 1, and the cumulative release on days 15 and 30 are significantly higher than that in Example 1. This indicates that the enzyme-containing foliar fertilizers prepared in Examples 6 and 7 were almost completely released by day 30 of the test, resulting in a poor slow-release effect. This is because the amount of grafted modified cyclodextrin added directly affects the encapsulation effect on the compound fertilizer, thus affecting the swelling rate, water retention rate, and slow-release capacity of the final enzyme-containing foliar fertilizer.

[0215] The test data from Examples 1, 8, and 9 show that the cumulative release of the enzyme-containing foliar fertilizers prepared in Examples 8 and 9 on days 15 and 30 was significantly higher than that in Example 1. This indicates that the enzyme-containing foliar fertilizers prepared in Examples 8 and 9 had almost completely released their contents by day 30, resulting in a poor slow-release effect. This is because the amount of hexadecyltrimethylammonium bromide added directly affects the intercalation effect on bentonite, thereby affecting the interlayer spacing of bentonite and preventing the modified bentonite from fully inhibiting the diffusion of the compound fertilizer.

[0216] The test data from Examples 1, 10, and 11 show that the swelling rate and water retention rate of the enzyme-containing foliar fertilizers prepared in Examples 10 and 11 are lower than those in Example 1, and the cumulative release on days 15 and 30 are significantly higher than that in Example 1. This indicates that the enzyme-containing foliar fertilizers prepared in Examples 10 and 11 were almost completely released by day 30 of the test, resulting in a poor slow-release effect. This is because the amount of sodium alginate added directly affects the swelling rate and water retention rate of the enzyme-containing foliar fertilizer, thus affecting its slow-release capacity.

[0217] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing an enzyme-containing foliar fertilizer to promote crop yield increase during the grain-filling stage, characterized in that, The preparation method includes: (I) A compound fertilizer is obtained by mixing nitrogen fertilizer, phosphorus fertilizer, potassium fertilizer, compound bacterial powder, and compound enzyme preparation. The compound bacterial powder includes Bacillus subtilis, Bacillus licheniformis, Bacillus mucilage, Bacillus megaterium, and lactic acid bacteria. The mass ratio of Bacillus subtilis, Bacillus licheniformis, Bacillus mucilage, Bacillus megaterium, and lactic acid bacteria in the compound bacterial powder is (1~1.5):(0.8~1.2):(0.6~0.9):(0.5~0.7):(1~1.2). The compound enzyme preparation includes pectinase, cellulase, and xylanase. The compound fertilizer is dispersed in Tween 20 solution and mixed evenly to obtain a fertilizer solution. (II) β-cyclodextrin is added to a silane coupling agent solution, mixed evenly, and then heated under reflux. The reaction product is filtered, washed, and dried to obtain amino-modified cyclodextrin. The amino-modified cyclodextrin is added to a polylactic acid solution, and after mixing and reaction, graft-modified cyclodextrin is obtained. The graft-modified cyclodextrin is dispersed in N,N-dimethylformamide to obtain a cyclodextrin solution. The fertilizer solution is added to the cyclodextrin solution, and the mass ratio of the compound fertilizer in the fertilizer solution to the graft-modified cyclodextrin in the cyclodextrin solution is 1:(10~20). After mixing evenly, the mixture is freeze-dried to obtain a coated modified compound fertilizer. (III) Bentonite is added to a silane coupling agent solution, heated and stirred to react, and the reaction product is filtered, washed and dried to obtain amino-modified bentonite; hexadecyltrimethylammonium bromide, polycarboxylic acid metal chelating agent and aluminum hydroxide pillar agent are dispersed in deionized water and mixed evenly to obtain a composite modified solution; the amino-modified bentonite is dispersed in deionized water and mixed evenly to obtain a bentonite suspension, and the composite modified solution is added dropwise to the bentonite suspension, wherein the mass ratio of hexadecyltrimethylammonium bromide to amino-modified bentonite in the bentonite suspension is (0.2-0.3):1, and stirring and heating are continued during the dropwise addition. After all the dropwise addition is completed, heating is continued for a period of time, and then the composite modified bentonite is obtained after filtration, washing and drying. (IV) Chitosan, sodium alginate, and deionized water are mixed and stirred until homogeneous to obtain a mixture; the coated modified compound fertilizer and the modified bentonite are added to the mixture, and the mixture is ultrasonically dispersed to obtain a composite sol. The mass ratio of chitosan, sodium alginate, coated modified compound fertilizer, and modified bentonite is (2~3):(0.4~0.5):10:(0.5~0.6); the composite sol is added dropwise to a calcium salt solution and soaked for a period of time to obtain a hydrogel microbead precursor. The mass fraction of the calcium salt solution is 2~3 wt%; the hydrogel microbead precursor is taken out and soaked in a sulfate solution to obtain composite hydrogel microbeads; the composite hydrogel microbeads are freeze-dried to obtain the enzyme-containing foliar fertilizer.

2. The preparation method according to claim 1, characterized in that, In step (I), the compound fertilizer comprises the following components in parts by weight: 30-40 parts nitrogen fertilizer; 20-30 parts phosphate fertilizer; 20-30 parts potassium fertilizer; 5-10 parts of compound bacterial powder; 3-8 portions of compound enzyme preparation.

3. The preparation method according to claim 1, characterized in that, In step (I), the nitrogen fertilizer includes any one or a combination of at least two of urea, ammonium sulfate, or ammonium nitrate. The phosphate fertilizer includes any one or a combination of at least two of superphosphate, monoammonium phosphate, or diammonium phosphate. The potassium fertilizer includes any one or a combination of at least two of potassium sulfate, potassium nitrate, potassium carbonate, or potassium chloride; In the compound enzyme preparation, the mass ratio of pectinase, cellulase and xylanase is (2~2.5):(1~1.5):(2.5~3); The compound fertilizer in the fertilizer solution has a mass fraction of 20-30 wt%.

4. The preparation method according to claim 1, characterized in that, In step (II), the silane coupling agent solution is composed of a silane coupling agent and an aqueous ethanol solution; The mass fraction of the silane coupling agent in the silane coupling agent solution is 10~20 wt%; The mass ratio of the β-cyclodextrin to the silane coupling agent in the silane coupling agent solution is 1:(0.1~0.5); The temperature of the heating reflux reaction is 50~60℃; The heating and reflux reaction time is 3-4 hours.

5. The preparation method according to claim 1, characterized in that, In step (II), the mass fraction of polylactic acid in the polylactic acid solution is 5-15 wt%. The mass ratio of the amino-enhanced cyclodextrin to the polylactic acid in the polylactic acid solution is (10~15):1; The mixing reaction temperature of the amino-substituted cyclodextrin and the polylactic acid solution is 70~80℃; The reaction time for the amino-modified cyclodextrin and the polylactic acid solution is 5-8 hours. The grafted modified cyclodextrin in the cyclodextrin solution has a mass fraction of 5-10 wt%. The freeze-drying temperature is -30~-20℃; The freeze-drying time is 1 to 3 hours.

6. The preparation method according to claim 1, characterized in that, In step (III), the silane coupling agent solution is composed of a silane coupling agent and an aqueous ethanol solution; The mass fraction of the silane coupling agent in the silane coupling agent solution is 10~20 wt%; The mass ratio of the bentonite to the silane coupling agent in the silane coupling agent solution is 1:(1.2~1.3); The reaction temperature between the bentonite and the silane coupling agent solution is 100~110℃; The reaction time between the bentonite and the silane coupling agent solution is 0.5~1.5h.

7. The preparation method according to claim 1, characterized in that, In step (III), the concentration of hexadecyltrimethylammonium bromide in the composite modified solution is 0.1~0.25 mol / L; The ratio of the polycarboxylated metal chelating agent to the amino-modified bentonite in the bentonite suspension is (0.3~0.8) mL:1 g; The polycarboxylated metal chelating agent includes any one or a combination of at least two of tetraethylenepentamine, triethylenetetramine, ethylenediamine or diethylenetriamine; The ratio of aluminum ions in the hydroxyaluminum pillar agent to amino-modified bentonite in the bentonite suspension is (1.0~1.5) mmol:1g. The mass fraction of amino-modified bentonite in the bentonite suspension is 1-5 wt%. The heating temperature is 50-60℃; After all the composite modified solution has been added dropwise, continue heating for 1-2 hours.

8. The preparation method according to claim 1, characterized in that, In step (IV), the concentration of chitosan in the mixture is 10~20 mg / mL; The ultrasonic power used for ultrasonic dispersion is 80~100kW; The ultrasonic dispersion process takes 1 to 3 hours.

9. The preparation method according to claim 1, characterized in that, In step (IV), the dropping rate of the composite sol is 0.1~0.2 mL / s; The immersion time of the composite sol droplets in the calcium salt solution is 10-20 minutes; The sulfate solution has a mass fraction of 2-3 wt%. The hydrogel microbead precursor was soaked in the sulfate solution for 10-20 minutes. The freeze-drying temperature of the composite hydrogel microspheres is -40~-20℃; The freeze-drying time for the composite hydrogel microspheres is 6-12 hours.

10. An enzyme-containing foliar fertilizer for promoting crop yield increase during the grain-filling stage, prepared by the preparation method according to any one of claims 1 to 9.

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