Preparation method and application of rhizosphere nutrient enrichment and signal induction growth promoter

Abstract

The invention relates to the technical field of agricultural production, and discloses a preparation method and application of a rhizosphere nutrient enrichment and signal induction growth promoter. The method comprises the following steps: chelating and concentrating potassium nitrate, monopotassium phosphate and the like with an EDTA-citric acid chelating agent under an alkaline condition; trace elements are chelated by amino acid, modified by polyglutamic acid and emulsified into a nano suspension; the oligosaccharide and the cyclodextrin are included, the hormone and the calcium alginate are embedded, and the PLGA coating is performed to form a three-layer microcapsule; and adding the materials into a carboxymethyl chitosan solution for granulation, sequentially coating a rapidly disintegrating film, a pH sensitive film and a cellulase response film, and drying to obtain the growth promoter. The technical problems that a traditional growth promoter is low in nutrient utilization rate, short in signal action time and poor in compatibility stability are solved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of agricultural production, in particular to a rhizosphere nutrition strengthening and signal induction growth agent preparation method and application thereof. BACKGROUND

[0002] The existing plant growth agent is prepared by directly mixing single nutrient elements, and the nutrient elements exist in the form of free state or simple salt, which is easy to react with anions such as phosphate and carbonate in the soil to form insoluble precipitates after being applied to the soil, thereby reducing the availability of the nutrient elements in the rhizosphere region. In addition, the signal molecules of plant hormones in the traditional growth agent are directly mixed, and the hormones are rapidly released in a short time after application, which causes the signal concentration to suddenly rise and fall, and the continuous activation of the plant growth channel cannot be maintained. Furthermore, the existing technology lacks a synergistic mechanism for the functions of nutrition supply and signal induction, and the absorption efficiency of the nutrient elements and the effect of the signal molecules are limited.

[0003] The existing technology has the following deficiencies: first, the traditional chelation process only uses a single chelating agent EDTA, without considering the affinity difference of different valence metal ions to the chelating agent, which leads to low chelation rate of some elements and easy dissociation of the chelates in the acidic environment of the rhizosphere; second, the particle size of the micronutrient element preparation is greater than 500 nanometers, which cannot efficiently penetrate the cell wall pore size of the roots, and the surface of the particles lacks rhizosphere targeting functional groups, which are randomly distributed in the soil and difficult to enrich in the rhizosphere; third, the signal molecules are directly added or use single-layer embedding technology, and the release curve is a simple diffusion mode, which cannot realize the time sequence synergistic activation of pioneer signal starting-bridge signal maintaining-continuous signal consolidating; fourth, the nutrition components and signal components are simply physically mixed, and the complexation and precipitation reaction between the metal ions and the hormone molecules leads to poor compatibility stability, and the loss of effective ingredients during the shelf life is more than 20%.

[0004] The construction of the EDTA-citric acid dynamic chelation balance system can solve the problem of poor selectivity of a single chelating agent for different valence metal ions, but how the nutrient solution after dynamic chelation and the micronutrient element nanoparticles are precisely positioned in the rhizosphere still needs to be solved. Further, even if the rhizosphere positioning is realized, how to synchronize the time sequence release of the signal molecules with the nutrition absorption process to produce a synergistic amplification effect is still a technical difficulty. More deeply, when the three components with different properties, i.e., the nutrient solution, the nanoparticles and the signal microcapsules, are compounded, how to prevent the cross-reaction between the metal ions and the signal molecules by the stabilizer system and maintain long-term stability during storage and use. SUMMARY

[0005] This application provides a method for preparing rhizosphere nutrient enhancement and signal-induced growth agents and their applications. The method utilizes EDTA-citric acid double chelating agent to construct dynamic equilibrium, polyglutamic acid nano-coating to achieve rhizosphere electrostatic targeting, three-layer gradient release microcapsules to achieve temporal signal activation, carboxymethyl chitosan zwitterionic crosslinking to achieve component compatibility stability, and three-layer intelligent response membrane to achieve rhizosphere microenvironment-triggered release. This method solves the technical problems of low nutrient utilization, short signal action time, and poor compatibility stability of traditional growth agents.

[0006] In a first aspect, this application provides a method for preparing rhizosphere nutrient enhancement and signal-induced growth agent, the method comprising: Step S1: Potassium nitrate, potassium dihydrogen phosphate, and magnesium sulfate are chelated with EDTA-citric acid double chelating agent under alkaline conditions, and then a dynamic chelation equilibrium is formed by pH adjustment and vacuum concentration to obtain chelated nutrient solution. Step S2: Ferrous sulfate, zinc sulfate, manganese sulfate, boric acid and sodium molybdate are chelated with amino acids, then polyglutamic acid is added for surface modification and high-speed shear emulsification to obtain a suspension of nano-chelated particles. Step S3: Oligosaccharides are encapsulated with cyclodextrin to form an immediate-release layer, hormone signaling molecules are encapsulated with calcium alginate gel to form a sustained-release layer, and then coated with PLGA solution to form a controlled-release layer, thus obtaining a three-layer gradient release microcapsule; Step S4: The chelated nutrient solution, the nano-chelated particle suspension, and the three-layer gradient release microcapsules are added to a carboxymethyl chitosan solution, mixed, and wet-granulated to obtain composite particles; Step S5: The composite particles are sequentially coated with a rapid-disintegration membrane, a pH-sensitive enteric membrane, and a cellulase-responsive membrane, and then dried and stabilized to obtain the target growth agent.

[0007] Secondly, the present invention provides an application of a rhizosphere nutrient fortification and signal-induced growth agent prepared according to a rhizosphere nutrient fortification and signal-induced growth agent preparation method in agricultural planting.

[0008] The technical solution provided in this application solves the problem of poor selectivity of traditional single chelating agents for metal ions of different valence states by chelating potassium nitrate, potassium dihydrogen phosphate, and magnesium sulfate with an EDTA-citric acid double chelating agent under alkaline conditions and forming a dynamic chelation equilibrium through pH control. In the double chelation system, the chelation stability constant of EDTA for high-valence iron and calcium ions is significantly higher than that of citric acid, while the chelation of magnesium ions by citric acid forms a dynamic equilibrium that can be dissociated in the rhizosphere. When the chelating solution is applied to the rhizosphere, the organic acids secreted by the roots cause the local pH to drop, and the citric acid-magnesium chelate partially dissociates to release magnesium ions to supply the roots. This technology utilizes EDTA-iron chelates for absorption, while maintaining stability under acidic conditions to prevent oxidation and precipitation. It achieves differentiated stability and responsive release of different elements. Furthermore, it employs a technique where ferrous sulfate, zinc sulfate, manganese sulfate, boric acid, and sodium molybdate are chelated with amino acids, then surface-modified with polyglutamic acid and subjected to high-speed shear emulsification to obtain a nano-chelated particle suspension. This process utilizes the amino and carboxyl groups of amino acids to form stable chelate ring structures with metal ions, followed by high-density carboxyl group coating on the polyglutamic acid side chains to form a negatively charged surface layer. The particle size is controlled within the range of 80 to 150 nanometers to match the pore size of root hair cell walls and the acidity of root hairs. At the microscale, electrostatic attraction between the negatively charged surface and the positively charged protonated amino groups on the root hair cell membrane enables targeted enrichment in the rhizosphere. This solves the problems of traditional micronutrient preparations having excessively large particle sizes that prevent efficient cell wall penetration and lack of directional rhizosphere migration. Furthermore, the technology utilizes a three-layer gradient release microcapsule technique: encapsulating oligosaccharides with cyclodextrin to form a rapid-release layer, embedding hormone signaling molecules with calcium alginate gel to form a sustained-release layer, and then coating with PLGA solution to form a controlled-release layer. The cyclodextrin-encapsulated oligosaccharides are rapidly released within 0 to 2 hours, acting as a pioneer signal to activate root cell membrane receptors and the MAPK signaling pathway, thereby promoting intracellular... Increased calcium ion concentration indicates a pre-activated signal state. Hormones embedded in calcium alginate gel are slowly released as bridging signals over 2 to 24 hours. As the root system is already in a pre-activated state, the hormone signal threshold decreases, resulting in a cross-enhancement effect that nonlinearly amplifies the expression of auxin response factors. The PLGA controlled-release layer continuously releases gibberellin as a maintenance signal over 24 to 72 hours. Furthermore, lactic acid, a degradation product of PLGA, slowly decreases the rhizosphere pH, promoting gibberellin protonation, increasing membrane permeability, and forming a self-enhancing cycle of release-acidification-absorption. This represents a breakthrough from simultaneous application and mutual antagonism of signal molecules to temporal separation and synergistic amplification.

[0009] Furthermore, the technical characteristics of obtaining composite particles by mixing chelated nutrient solution, nano-chelated particle suspension, and three-layer gradient release microcapsules in a carboxymethyl chitosan solution and wet granulating are as follows: the carboxymethyl chitosan molecular chain simultaneously contains cationic amino groups and anionic carboxyl groups, exhibiting an amphoteric state. The cationic amino groups bind to the negatively charged surface of the metal chelate in the chelated nutrient solution through electrostatic attraction, and simultaneously bind to the negatively charged polyglutamic acid layer on the surface of the nano-chelated particles. The anionic carboxyl groups bind to the terminal carboxyl groups of the PLGA coating layer on the surface of the three-layer gradient release microcapsules through hydrogen bonding. The amphoteric structure allows carboxymethyl chitosan to act as a "molecular bridge" between different components, achieving dynamic stability. Combined with the layered silicate structure of modified bentonite, it provides a huge specific surface area for adsorbing and fixing nutrient elements, solving the problem of poor compatibility stability caused by the cross-complexation and precipitation of metal ions and signal molecules in traditional simple mixing processes. Finally, the composite particles are sequentially coated with a rapid-disintegration membrane, a pH-sensitive enteric membrane, and a cellulase-responsive membrane. The technical characteristics of obtaining the target growth agent after coating and drying stabilization are as follows: In the rapid-disintegrating membrane, hydroxypropyl methylcellulose rapidly disintegrates within 2 minutes in the pH range of 5.5 to 7.0, allowing the particles to fully contact the soil. In the pH-sensitive enteric membrane, the carboxyl groups of the methacrylic acid copolymer are protonated and insoluble at pH less than 6.0, inhibiting release. When the rhizosphere pH is greater than 6.5, the carboxyl groups deprotonate, the membrane layer swells and dissolves, and release is initiated. The carboxylmethyl cellulose "bridge" structure pre-embedded in the cellulase-responsive membrane is hydrolyzed by cellulase secreted by rhizosphere microorganisms, causing the chitosan membrane network to rupture. Moreover, the enzyme activity enhancement has rhizosphere spatial selectivity, occurring only around active root segments that secrete large amounts of carbon sources. The three-layer coating structure realizes an intelligent multi-level release mode of rapid initiation-pH-responsive slow release-microorganism-triggered controlled release, synchronizing nutrient and signal release behavior with the root growth rhythm, fundamentally solving the core problem of low nutrient utilization and poor signaling effect caused by the mismatch between the release and demand of traditional growth agents. Attached Figure Description

[0010] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 This is a schematic diagram of one embodiment of the rhizosphere nutrient enhancement and signal-induced growth agent preparation method in this application; Figure 2 This is a schematic diagram of the cumulative release curve of the three-layer gradient release microcapsules in the embodiments of this application. Detailed Implementation

[0012] This application provides a method for preparing rhizosphere nutrient enhancement and signal-induced growth agents, and its application. The terms "first," "second," "third," "fourth," etc. (if present) in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in a sequence other than that illustrated or described herein. Furthermore, the terms "comprising" or "having" and any variations thereof are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0013] For ease of understanding, the specific process of the embodiments of this application is described below. Please refer to [link / reference]. Figure 1 One embodiment of the rhizosphere nutrient enhancement and signal-induced growth agent preparation method in this application includes: Step S1: Potassium nitrate, potassium dihydrogen phosphate, and magnesium sulfate are chelated with EDTA-citric acid double chelating agent under alkaline conditions, and then a dynamic chelation equilibrium is formed by pH adjustment and vacuum concentration to obtain chelated nutrient solution. Step S2: Ferrous sulfate, zinc sulfate, manganese sulfate, boric acid and sodium molybdate are chelated with amino acids, then polyglutamic acid is added for surface modification and high-speed shear emulsification to obtain a suspension of nano-chelated particles. Step S3: Oligosaccharides are encapsulated with cyclodextrin to form an immediate-release layer, hormone signaling molecules are encapsulated with calcium alginate gel to form a sustained-release layer, and then coated with PLGA solution to form a controlled-release layer, thus obtaining a three-layer gradient release microcapsule; Step S4: Add the chelated nutrient solution, the nano-chelated particle suspension and the three-layer gradient release microcapsules into the carboxymethyl chitosan solution, mix and wet granulate to obtain composite particles; Step S5: The composite particles are sequentially coated with a rapid-disintegration membrane, a pH-sensitive enteric membrane, and a cellulase-responsive membrane, followed by drying and stabilization to obtain the target growth agent.

[0014] It is understood that the executing entity of this application can be a rhizosphere nutrient enhancement and signal-induced growth agent preparation system, or it can be a terminal or a server; the specific implementation is not limited here. This application's embodiments use a server as an example for illustration.

[0015] Specifically, step S1 achieves the preparation of stable-state nutrients through a dynamic chelation equilibrium mechanism. First, 120g of potassium nitrate, 80g of potassium dihydrogen phosphate, and 55g of magnesium sulfate are dissolved in 800ml of deionized water and stirred at 25℃ for 30 minutes to form an aqueous solution of nutrients. At this point, potassium ions, magnesium ions, and phosphate ions are in a free state. Then, 45g of disodium EDTA is added dropwise at a mass ratio of 1:0.15, and the pH is simultaneously adjusted to the range of 7.2-7.5 to obtain the EDTA chelation reaction solution. The carboxyl groups of EDTA form coordination bonds with metal ions, converting potassium and magnesium ions into a chelated state. When the pH titration curve is monitored, the rate of pH change is observed to increase from the initial 0. When the concentration of EDTA decreased from 0.15 units to 0.03 units, it indicated that the EDTA chelation reaction was close to equilibrium. At this point, 30 grams of citric acid were added and the pH was maintained at 7.35. The three carboxyl groups of citric acid formed a 1:1 coordination chelate with the remaining free magnesium ions. Since the chelation stability constants of EDTA for iron and calcium ions were 25.1 and 10.7, respectively, which were much higher than those of citric acid (11.4 and 3.5), while the chelation stability constant of citric acid for magnesium ions (3.4) was only slightly different from that of EDTA (8.7), the two formed a competitive chelation dynamic equilibrium for magnesium ions. Finally, the double chelation reaction solution was concentrated to 75% of the initial volume (600 ml) under vacuum at 60°C to obtain the chelated nutrient solution.

[0016] Step S2 utilizes nanotechnology to achieve rhizosphere-targeted delivery of trace elements. First, 2.5 g of ferrous sulfate, 1.8 g of zinc sulfate, 1.2 g of manganese sulfate, 0.8 g of boric acid, and 0.6 g of sodium molybdate are dissolved in 200 mL of deionized water to obtain a trace element aqueous solution. Then, 12 g of a compound amino acid chelating agent with a glycine to glutamic acid mass ratio of 3:2 is added, and the pH is adjusted to 8.0-8.5 to initiate the chelation reaction. The amino and carboxyl groups of the amino acids form stable five- or six-membered chelate rings with metal ions, achieving chelation rates of 88%, 91%, and 86% for iron, zinc, and manganese ions, respectively, to obtain an amino acid chelate solution. Finally, a chelating agent with a molecular weight of 15000-250 is added to the amino acid chelate solution. Three grams of 00 Dalton polyglutamic acid were used, and the pH was adjusted to 6.8-7.2 to dissociate the carboxyl groups of the polyglutamic acid side chains and form a negatively charged coating layer to obtain a surface-modified chelate solution. Each nanometer segment of the polyglutamic acid side chain contains 8-12 carboxyl groups, which adsorb the formed amino acid-metal chelate through electrostatic interaction. The surface-modified chelate solution was sheared for 20 minutes at 12,000 rpm using a high-speed shear emulsifier, and the particle size distribution was detected by a dynamic light scattering instrument. When the particle size was found to be concentrated in the range of 80-150 nanometers and the Z potential was negative 28 mV, the shearing was stopped to obtain a nano-chelate particle suspension. The negatively charged surface and the protonated amino groups on the surface of plant root cell membranes generate electrostatic attraction to achieve directional enrichment in the rhizosphere.

[0017] Step S3 utilizes a three-layer coating technique to achieve the time-sequential release of signal molecules. First, 5 g of chitosan oligosaccharide and 3 g of alginate oligosaccharide are dissolved in 100 mL of pH 5.5 acetate buffer solution. Then, 50 mL of a 100 g / L β-cyclodextrin aqueous solution is added, and the mixture is stirred at 40°C for 2 hours to form an inclusion complex. Oligosaccharide molecules enter the cyclodextrin cavity through hydrogen bonding to form an inclusion complex. After cooling to 15°C, white crystals precipitate, which are then filtered and dried to obtain 8.2 g of oligosaccharide inclusion complex rapid-release particles. These particles exhibit an 80% release rate in water within 10 minutes and serve as the rapid-release precursor signal layer. 0.8 g of indoleacetic acid, 0.6 g of benzylaminopurine, and 0.4 g of gibberellin are dissolved in 50 mL of anhydrous ethanol to form a hormone mixture. This mixture is then mixed with 20 g of a 30 g / L sodium alginate solution and injected dropwise at a rate of 0.5 mL / min using a syringe pump. In 200 ml of calcium chloride solution per liter, sodium alginate undergoes an instantaneous ion exchange gelation reaction with calcium ions to form hormone-encapsulated gel microspheres with a particle size of 2-3 mm, thus obtaining a sustained-release bridging signal layer. 15 g of polylactic acid-glycolic acid copolymer is dissolved in 80 ml of dichloromethane to form a PLGA organic phase. The hormone-encapsulated gel microspheres are added to the PLGA organic phase, and 3 g of polyvinyl alcohol aqueous solution with a concentration of 30 g / L is added. The mixture is emulsified for 10 minutes at 8000 rpm in a high-speed homogenizer to form a water-in-oil-in-water double emulsion system. The mixture is then transferred to 500 ml of distilled water and stirred at 25°C to evaporate the dichloromethane for 4 hours, allowing PLGA to deposit and solidify on the surface of the microspheres to form a controlled-release maintenance signal layer with a thickness of 50-80 micrometers. The oligosaccharide inclusion complex rapid-release particles are mixed with the PLGA-coated microspheres at a mass ratio of 1:3 to obtain a three-layer gradient release microcapsule.

[0018] Step S4 achieves physical isolation of nutrients and signals through the zwitterionic crosslinking of carboxymethyl chitosan. First, 25 g of carboxymethyl chitosan is added to 200 mL of deionized water, and the pH is adjusted to 4.5-5.0 using acetic acid solution to protonate the amino groups and promote dissolution, obtaining a carboxymethyl chitosan solution. Then, 15 g of sodium montmorillonite bentonite is organically modified with hexadecyltrimethylammonium bromide at 80 °C, increasing the interlayer spacing from 1.2 nm to 3.8 nm. After washing and drying, modified bentonite is obtained. The modified bentonite is added to the carboxymethyl chitosan solution and ultrasonically dispersed for 30 minutes under high-speed stirring at 1000 rpm until the bentonite interlayer spacing is further increased, obtaining a bentonite dispersion. The surface potential of the bentonite dispersion is measured to be -22 mV using a Zeta potential analyzer, and the pH is adjusted to 6.8-7.2 to deprotonate the amino groups of carboxymethyl chitosan and dissociate the carboxyl groups, forming a zwitterionic state, thus obtaining carboxymethyl chitosan. A polysaccharide stabilizer mixture was prepared by sequentially adding 600 ml of chelated nutrient solution, 200 ml of nano-chelated particle suspension, and 50 g of three-layer gradient release microcapsules at a mass ratio of 85:15 to a carboxymethyl chitosan stabilizer mixture and premixing at 500 rpm for 5 minutes to obtain a composite slurry. The cationic amino groups on the carboxymethyl chitosan molecular chain adsorb negatively charged nano-chelated particles through electrostatic interaction, while the anionic carboxyl groups stabilize the surface of the PLGA microcapsules through hydrogen bonding to form a steric hindrance protective layer. 80 ml of hydroxypropyl methylcellulose binder solution with a concentration of 50 g / L was sprayed into the composite slurry through an atomizing nozzle, and the mixture was sheared and granulated at 1200 rpm in a high-speed mixer for 12 minutes. Under the combined action of mechanical shearing force and liquid bridge adhesion force, spherical particles with a particle size of 1.5-3.0 mm were formed. The wet-granulated particles were then collected by vibratory sieving, and particles with a particle size range of 2.0-3.5 mm were obtained to obtain composite particles.

[0019] Step S5 achieves responsive release to the rhizosphere microenvironment through a three-layer intelligent coating. First, 8 grams of hydroxypropyl methylcellulose, 2 grams of polyethylene glycol 400 as a plasticizer, and 1 gram of talc as a flow aid are dissolved in 100 ml of distilled water to form a rapid-disintegrating film coating solution. This solution is then sprayed onto the surface of the composite particles for 18 minutes at an inlet air temperature of 55°C and an outlet air temperature of 42°C, using a fluidized bed coating machine at an atomization pressure of 0.25 MPa and a spray rate of 4 ml / min, forming a rapid-disintegrating film layer with a thickness of 20-30 micrometers. This film layer rapidly disintegrates within 2 minutes within a pH range of 5.5-7.0. Finally, 12 grams of methacrylic acid copolymer, 3 grams of triacetin as a plasticizer, and 0.5 grams of titanium dioxide as a light-blocking agent are dissolved in 120 ml of water. An enteric coating solution was formed in an ethanol-water mixture (7:3 volume ratio). This solution was sprayed onto the surface of rapidly disintegrating membrane-coated particles at a rate of 5 ml / min under fluidized bed conditions reduced to 48°C for 25 minutes, forming an enteric-coated sustained-release membrane with a thickness of 40-60 micrometers. The surface roughness Ra value was measured to be 8.5 nanometers using atomic force microscopy, yielding the enteric-coated particles. The carboxyl groups of the methacrylic acid copolymer were protonated and insoluble at pH less than 6.0, and deprotonated and swelled at pH greater than 6.5, resulting in dissolution. Chitosan was cross-linked with glutaraldehyde to achieve a cross-linking degree of 25%, then mixed with 5 g of sodium alginate and 2 g of sodium carboxymethyl cellulose and dissolved in 150 ml of pH 4.5 acetic acid solution to form an enzyme-responsive membrane coating solution. This solution was sprayed onto the surface of the enteric-coated particles, and the coating was then analyzed by concentration measurement. Neutralization with 5 g / L sodium hydroxide atomized solution deprotonates the chitosan amino groups, causing in-situ deposition on the particle surface to form a 60-90 μm thick bioresponsive membrane, resulting in three-layer coated particles. Carboxymethyl cellulose is embedded in the chitosan network as a biodegradable bridge. The three-layer coated particles are evenly spread on a stainless steel tray with a thickness not exceeding 3 cm and placed in a vacuum drying oven at -0.08 MPa and 45°C for 6 hours, turning them every 2 hours until the moisture content drops to 2.3%, resulting in dried coated particles. 3 g ascorbic acid, 2 g tocopherol, 1 g propyl gallate, and 0.5 g ethoxyquinoline are dissolved in 100 mL of anhydrous ethanol to form an antioxidant protective solution, which is sprayed onto the dried coated particles through an ultrafine atomizing nozzle with droplet diameters less than 50 μm. Antioxidant-treated particles are obtained by drying the membrane particles on the surface of the particles in a fluidized bed at 45°C for 15 minutes to form a transparent antioxidant protective film with a thickness of 5-10 micrometers. 5 grams of lecithin, 3 grams of dehydrated sorbitan monostearate, and 2 grams of polysorbate are mixed at a mass ratio of 3:2 and dissolved in 120 ml of isopropanol-water mixture at a volume ratio of 1:1 to form a surfactant solution. This solution is sprayed onto the surface of the antioxidant-treated particles and dried at 40°C for 20 minutes. The contact angle of the particle surface is then measured using a contact angle meter, showing a decrease from 85 degrees to 32 degrees, resulting in surface-modified particles. These surface-modified particles are then fed into a roller extrusion granulator and extruded at a roller pressure of 15 MPa and a roller speed of 80 rpm to increase the particle bulk density from 0.68 g / cm³ to 0.The target growth agent was obtained by collecting particles with a diameter of 2.0-3.5 mm (92 grams per cubic centimeter) after vibrating sieving and achieving a hardness of 25 Newtons as measured by a hardness tester.

[0020] In one specific embodiment, step S1 includes: Potassium nitrate, potassium dihydrogen phosphate and magnesium sulfate were dissolved in deionized water and stirred at a constant temperature to obtain an aqueous solution of nutrients. Add disodium EDTA dropwise to the nutrient element aqueous solution according to the set mass ratio and simultaneously adjust the pH value to the alkaline range to obtain the EDTA chelation reaction solution. The pH change rate of the EDTA chelation reaction solution was monitored by pH titration curve. When the pH change rate was lower than the set threshold, citric acid was added and the pH value was kept stable to obtain the double chelation reaction solution. The double chelate reaction solution was heated and concentrated under vacuum to a predetermined ratio of its initial volume to obtain a chelated nutrient solution.

[0021] Specifically, the stabilization of three-layer coated particles was achieved through four consecutive processes: vacuum drying, antioxidant protection, surface activity modification, and mechanical curing. First, the three-layer coated particles were laid on a stainless steel tray with a thickness controlled to no more than 3 cm and placed in a vacuum drying oven. The vacuum level was set to -0.08 MPa, the temperature to 45°C, and the drying time to 6 hours. The particles were turned over every 2 hours. The moisture content was measured using the Karl Fischer moisture assay and found to have decreased to 2.3%. At this point, the porosity of the coating layer decreased from the initial 15% to 8%, and the membrane density increased. This is because the diffusion rate of water molecules from the inside of the membrane layer is accelerated under vacuum negative pressure, and the polymer chains in the membrane layer rearrange in an anhydrous state to form a more compact packing structure. Next, an antioxidant protective solution was prepared by dissolving 3 g of L-ascorbic acid, 2 g of tocopherol, 1 g of propyl gallate, and 0.5 g of ethoxyquinoline in 100 ml of anhydrous ethanol. The solution was then sprayed onto the surface of the dried particles through an ultrafine atomizing nozzle at a droplet diameter of less than 50 micrometers and a spraying rate of 1.5 ml / min. The particles were then dried in a fluidized bed at 45°C for 15 minutes to form a transparent protective film with a thickness of 5-10 micrometers. The antioxidant mechanism is that the enediol structure of L-ascorbic acid scavenges free radicals through electron donation, the phenolic hydroxyl group of tocopherol captures lipid peroxidation free radicals, the three ortho-hydroxyl groups of propyl gallate synergistically enhance the effect, and the quinoline ring structure of ethoxyquinoline blocks the oxidation chain reaction. After 30 days of accelerated oxidation at 60°C and 75% relative humidity, the retention rate of the signal molecule activity increased from 62% in the untreated group to 91%. The surfactant solution was prepared again. 5 grams of lecithin was used as a natural zwitterionic surfactant. 3 grams of dehydrated sorbitan monostearate (HLB value 4.7) and 2 grams of polysorbate 80 (HLB value 15) were mixed in a 3:2 ratio to form an emulsion system with an HLB value of 8.5. This system was dissolved in 120 ml of isopropanol-water (volume ratio 1:1) mixed solvent and sprayed onto the particle surface at a rate of 2 ml / min. After drying at 40°C for 20 minutes, the contact angle between the particle surface and water was measured using a contact angle meter, and the contact angle decreased from 85 degrees (untreated) to 32 degrees. The hydrophobic ends of the surfactant layer were adsorbed onto the particle coating layer through the hydrophobic interaction of the alkyl chains, while the polar groups of the hydrophilic ends faced outwards, thus shortening the wetting and disintegration time of the particles in the soil solution from 8 minutes to 1 minute. Finally, the processed granules are fed into a double-roller extrusion granulator. The roller pressure is set at 15 MPa, the roller speed at 80 rpm, and the roller gap at 2.5 mm. Under the extrusion of the double rollers, the internal voids of the granules are compressed, and the bulk density increases from 0.68 g / cm³ to 0.92 g / cm³. The compressive strength of a single particle is measured to be 25 Newtons (meaning that the particle will only break when subjected to an external force of 25 Newtons). The increase in compressive strength is due to the mechanical compaction, which makes the internal components of the granules more closely connected, reduces porosity, and makes the structure more compact. The qualified granules with a particle size of 2.0-3.0 mm are collected by vibrating screen and used as the target growth agent. The entire stabilization treatment extends the product shelf life from the conventional 3 months to 12 months.

[0022] In one specific embodiment, step S2 includes: Ferrous sulfate, zinc sulfate, manganese sulfate, boric acid, and sodium molybdate are dissolved in deionized water to obtain an aqueous solution of trace elements. Add a compound amino acid chelating agent of glycine and glutamic acid to an aqueous solution of trace elements and adjust the pH value to the alkaline range to carry out the chelation reaction to obtain an amino acid chelated solution. Polyglutamic acid was added to the amino acid chelation solution and the pH was adjusted to the neutral range to cause the carboxyl groups of the polyglutamic acid side chain to dissociate and form a negatively charged coating layer, thus obtaining a surface-modified chelation solution. The surface-modified chelate solution was sheared at a set speed using a high-speed shear emulsifier, and the particle size distribution was detected to the nanoscale range using a dynamic light scattering instrument to obtain a nano-chelate particle suspension.

[0023] Specifically, the key to preparing the nano-chelated particle suspension lies in three consecutive processes: amino acid chelation, polyglutamic acid surface modification, and high-speed shearing nano-sizing. First, 2.5 g of ferrous sulfate, 1.8 g of zinc sulfate, 1.2 g of manganese sulfate, 0.6 g of sodium molybdate, and 0.8 g of boric acid are weighed and dissolved in 200 mL of deionized water. The solution is stirred until completely dissolved to form an aqueous solution of trace elements. At this point, iron ions exist as Fe2+, zinc ions as Zn2+, and manganese ions as Mn2+. Next, 12 grams of a compound amino acid chelating agent with a glycine to glutamic acid mass ratio of 3:2 was added to the aqueous solution. The glycine molecule contains both an amino group (NH₂) and a carboxyl group (COOH), while the glutamic acid molecule contains one amino group and two carboxyl groups. The pH was adjusted to an alkaline range of 8.0 to 8.5 using sodium hydroxide solution. At this point, the lone pair electrons of the nitrogen atom in the amino group and the lone pair electrons of the oxygen atom in the carboxyl group simultaneously form coordinate bonds with the empty orbitals of the metal ions. Glycine forms a five-membered chelate ring with iron ions, and glutamic acid forms a six-membered chelate ring with zinc ions. After the chelation reaction proceeded for 15 minutes, the solution was purified. The chelation rates of iron, zinc, and manganese were determined by EDTA titration. The titration procedure was as follows: 1 mL of chelating solution was diluted to 50 mL, pH 10 ammonia buffer solution and Eriochrome Black T indicator were added, and titrated with 0.01 mol / L EDTA standard solution until the solution changed from wine red to pure blue. The volume of EDTA consumed was recorded. The concentration of unchelated metal ions was equal to the volume of EDTA consumed multiplied by the EDTA concentration. The chelation rate was equal to the original metal ion concentration minus the concentration of unchelated metal ions and then divided by the original metal ion concentration. The chelation rates of iron, zinc, and manganese were measured to be 88%, 91%, and 86%, respectively. Add 12 grams of polyglutamic acid to the amino acid chelate solution again. Polyglutamic acid is a biopolymer composed of glutamic acid units polymerized by peptide bonds, with a molecular weight of 15,000 to 25,000 Daltons. Its side chains contain a large number of carboxyl groups. Adjust the pH to a neutral range of 6.8 to 7.2 using hydrochloric acid solution. At this point, the carboxyl groups on the polyglutamic acid side chains undergo a dissociation reaction, changing from negative COOH to negative COO+H+. The degree of carboxyl dissociation is determined by potentiometric titration. Take 10 ml of the polyglutamic acid solution and adjust the pH to 3.0 with hydrochloric acid to completely protonate the carboxyl groups. Then titrate with a standard sodium hydroxide solution and record the pH change curve. At pH 6... The number of carboxyl groups dissociated corresponding to the volume of sodium hydroxide consumed in the range of 0.8 to 7.2 was calculated to be 92% dissociation. The dissociated carboxyl anions were adsorbed on the surface of the amino acid-metal chelate through electrostatic interaction to form a negative charge coating layer. The particle surface potential was measured to be -28 mV by a Zeta potential analyzer. The negative charge density was calculated by diluting 1 mL of surface-modified chelate solution to the standard concentration and injecting it into the sample cell of the Zeta potential analyzer. The sample was irradiated with laser to generate scattered light. The particle movement speed in the electric field was proportional to the surface potential. The instrument calculated the electrophoretic mobility by Doppler frequency shift and then converted it into Zeta potential.Finally, the surface-modified chelate solution was poured into a high-speed shear emulsifier, with the speed set at 12,000 rpm for 20 minutes. A strong shear force field was formed between the high-speed rotating rotor and stator. The shear stress equals the dynamic viscosity multiplied by the velocity gradient, and the velocity gradient equals the rotor linear velocity divided by the rotor-stator gap. When the shear stress exceeds the binding strength of the particle aggregates, the aggregates are broken down into smaller particles. Simultaneously, the polyglutamic acid coating layer is further uniformly distributed on the particle surface under high shear. During the shearing process, samples were taken every 5 minutes to detect the particle size distribution using a dynamic light scattering instrument. The principle of dynamic light scattering is that laser irradiation of particles in the suspension produces scattered light. The Brownian motion of the particles causes the intensity of the scattered light to fluctuate over time; smaller particles move faster and have a higher fluctuation frequency, while larger particles move slower and have a lower fluctuation frequency. The instrument... The particle diffusion coefficient was calculated by analyzing the scattered light intensity fluctuation characteristics using the autocorrelation function. Then, the diffusion coefficient was converted into a hydrodynamic diameter according to the Stokes-Einstein equation. The test results showed that the average particle size was 320 nm after 5 minutes of shearing, 195 nm after 10 minutes of shearing, 128 nm after 15 minutes of shearing, and the particle size stabilized in the range of 80 to 150 nm after 20 minutes of shearing. The particle size distribution index was less than 0.3, indicating uniform distribution. At this time, the nano-chelated particle suspension obtained had a spherical core-shell structure. The core was an amino acid-metal chelate, and the shell was a polyglutamic acid negative charge coating layer. The negative charge surface generated electrostatic repulsion between particles to prevent aggregation. At the same time, the negative charge generated electrostatic attraction with the positive charge of protonated amino groups on the surface of plant root cell membranes to achieve targeted enrichment in the rhizosphere.

[0024] In one specific embodiment, step S3 includes: Chitosan oligosaccharide and alginate oligosaccharide were dissolved in acetate buffer, and then β-cyclodextrin aqueous solution was added. The mixture was stirred at a set temperature to induce an inclusion reaction. After cooling, crystals were precipitated and filtered and dried to obtain oligosaccharide inclusion complex immediate-release particles. Indoleacetic acid, benzylaminopurine and gibberellin were dissolved in anhydrous ethanol to form a hormone mixture, which was then mixed with sodium alginate solution and injected into calcium chloride solution via an injection pump for cross-linking and gelation to obtain hormone-encapsulated gel microspheres. Polylactic acid-glycolic acid copolymer was dissolved in dichloromethane to form a PLGA organic phase. Hormone-encapsulated gel microspheres were added to the PLGA organic phase and polyvinyl alcohol aqueous solution was added. The mixture was emulsified in a high-speed homogenizer to form a complex emulsion system. The system was then transferred to distilled water and stirred to evaporate the organic solvent, allowing PLGA to be deposited and solidified on the surface of the microspheres to obtain PLGA-coated microspheres. Oligosaccharide inclusion complex immediate-release particles were mixed with PLGA-coated microspheres at a set mass ratio to obtain three-layer gradient release microcapsules.

[0025] Specifically, to prepare the immediate-release layer, 5 grams of chitosan oligosaccharide (degree of polymerization 3 to 7, degree of deacetylation above 85%) and 3 grams of alginate oligosaccharide (molecular weight 800 to 1200 Daltons) were dissolved in 100 ml of pH 5.5 acetate buffer. The acetate buffer was prepared by mixing acetic acid and sodium acetate in a specific ratio to stabilize the pH at 5.5. Oligosaccharides are protonated and positively charged under weakly acidic conditions, which facilitates dissolution. 5 grams of β-cyclodextrin aqueous solution (concentration 100 g / L) were added to this solution. β-cyclodextrin is a cyclic molecule formed by seven glucose units linked by α-1,4 glycosidic bonds, with an inner diameter of 0.6 to 0.8 nm and an outer diameter of 1.5 nm, and is hydrophobic. The cavity can encapsulate oligosaccharide molecules. The inclusion reaction is carried out by stirring in a 40°C water bath for 2 hours. During the inclusion process, oligosaccharide molecules enter the cyclodextrin cavity through van der Waals forces and hydrogen bonds. The inclusion stability constant is determined by fluorescence spectroscopy. The fluorescence intensity of the oligosaccharide solution before the addition of cyclodextrin is recorded as the baseline value. After the addition of cyclodextrin, the fluorescence intensity decreases as the oligosaccharide molecules enter the hydrophobic cavity. The amount of inclusion compound formed is calculated based on the fluorescence intensity change curve. After 2 hours of reaction, the solution is cooled to 15°C. The decrease in temperature causes the solubility of the inclusion compound to decrease, and white crystals precipitate from the solution. The crystals are collected by filtration through a Buchner funnel and dried to constant weight in a 60°C oven. 8.2 grams of oligosaccharide inclusion compound instant-release granules are obtained. Next, a sustained-release layer was prepared. 0.8 g of indoleacetic acid (an auxin-like hormone), 0.6 g of benzylaminopurine (a cytokinin-like hormone), and 0.4 g of gibberellin were dissolved in 50 mL of anhydrous ethanol to form a hormone mixture. The three hormones have high solubility and stability in ethanol. 20 g of sodium alginate solution (30 g / L) was prepared separately. Sodium alginate is a linear polysaccharide composed of β-D-mannuronic acid and α-L-guluronic acid linked by 1,4-glycosidic bonds. The carboxyl groups on the molecular chain can undergo ion exchange with calcium ions. The hormone mixture was slowly poured into the sodium alginate solution. The hormone was uniformly dispersed by stirring while turning the liquid. The mixture was then dropped into 200 ml of calcium chloride solution (concentration 20 g / L) using a syringe pump (flow rate 0.5 ml / min). Upon contact with the calcium solution, the droplets underwent a gelation reaction. The carboxyl anions on the sodium alginate molecular chains coordinated with calcium ions to form an eggshell structure. Adjacent molecular chains were cross-linked into a three-dimensional network through calcium ion bridges. The hormone molecules were embedded in the pores of the gel network. The diameter of the gel microspheres was measured to be 2 to 3 mm using a microscope. The microspheres were collected and rinsed three times with deionized water to remove residual calcium ions from the surface, resulting in hormone-encapsulated gel microspheres.To prepare the controlled-release layer again, 15 grams of polylactic acid-glycolic acid copolymer (lactic acid to glycolic acid molar ratio 75:25, molecular weight 30,000 Daltons) was weighed and dissolved in 80 ml of dichloromethane to form the PLGA organic phase. PLGA is a biodegradable polymer material; its ester bonds break and degrade under the action of hydrolytic enzymes, and the degradation rate is related to the ratio of lactic acid to glycolic acid. Hormone-encapsulated gel microspheres were added to the PLGA organic phase, along with 3 grams of polyvinyl alcohol (molecular weight 88,000 to 98,000, degree of polymerization 1750±50) aqueous solution as an emulsifying stabilizer. The hydroxyl groups in the polyvinyl alcohol molecular chain are hydrophilic, while the carbon chains are hydrophobic, resulting in directional alignment at the oil-water interface and reducing interfacial tension. Emulsification was performed for 10 minutes using a high-speed homogenizer (8000 rpm). The oil phase was dispersed into tiny droplets to encapsulate the aqueous phase gel microspheres, forming a water-in-oil-in-water double emulsion system. The diameter of the double emulsion droplets ranged from 5 to 20 micrometers. The double emulsion system was slowly poured into 500 ml of distilled water and stirred at room temperature (300 rpm) for 4 hours. During the stirring process, the volatilization rate of dichloromethane was controlled by temperature and stirring rate. Dichloromethane has a boiling point of 39.6℃, a density of 1.33 g / cm³, and low solubility in water. During the volatilization process, PLGA molecules gradually precipitated from the organic phase and deposited on the surface of the gel microspheres. The deposition rate was related to the volatilization rate of dichloromethane. After complete volatilization, PLGA formed a dense coating layer on the surface of the microspheres. The thickness of the coating layer was measured to be 50 to 80 micrometers by scanning electron microscopy of the microsphere cross-section, thus obtaining PLGA-coated microspheres. Finally, the oligosaccharide inclusion complex immediate-release particles and PLGA-coated microspheres were mixed at a mass ratio of 25:75. The mixing ratio was optimized based on release kinetics. The immediate-release layer rapidly releases oligosaccharide signaling molecules from 0 to 2 hours, the sustained-release layer in the PLGA-coated microspheres releases hormone signals from 2 to 24 hours, and the controlled-release layer continuously releases signals from 24 to 72 hours. The three-layer structure achieves the time-sequential release of signaling molecules, resulting in three-layer gradient release microcapsules.

[0026] Figure 2 This is a schematic diagram of the cumulative release curve of the three-layer gradient release microcapsules in the embodiments of this application; Figure 2The in vitro cumulative release curves of the three-layer gradient release microcapsules in this embodiment are shown. The solid line represents the release curve of the immediate-release layer (oligosaccharide inclusion complex), the dashed line represents the release curve of the sustained-release layer (hormone-encapsulated gel microspheres), and the dotted line represents the release curve of the controlled-release layer (PLGA-coated microspheres). As can be seen from the figure, the immediate-release layer rapidly releases over 90% of its cumulative release within 0 to 2 hours, acting as a pioneer signal to activate root cell membrane receptors; the sustained-release layer slowly releases over 2 to 24 hours, with a cumulative release rate of 85%, acting as a bridging signal to maintain auxin response factor expression; and the controlled-release layer continuously releases over 24 to 72 hours, with a cumulative release rate of 82%, acting as a maintenance signal to consolidate growth pathway activation. This three-layer gradient release structure represents a breakthrough from simultaneous application and mutual antagonism of signaling molecules to temporal separation and synergistic amplification, transforming the signal action time from the traditional short-term rapid rise and fall to a continuous 72-hour gradient activation mode.

[0027] In one specific embodiment, step S4 includes: Carboxymethyl chitosan was dissolved in deionized water and modified bentonite was added and stirred to disperse, thus obtaining a carboxymethyl chitosan stabilizer mixture. Chelated nutrient solution, nano-chelated particle suspension and three-layer gradient release microcapsules were sequentially added to carboxymethyl chitosan stabilizer mixture at a set mass ratio and premixed at a set speed to obtain composite slurry. Hydroxypropyl methylcellulose binder solution is sprayed into the composite slurry through an atomizing nozzle and then sheared and granulated in a high-speed mixer to obtain wet-granulated particles. The wet-granulated particles are vibrated and screened to collect particles within a set particle size range to obtain composite particles.

[0028] Specifically, to prepare a carboxymethyl chitosan stabilizer mixture, weigh 25 grams of carboxymethyl chitosan and add it to 200 ml of deionized water. Carboxymethyl chitosan is a derivative of chitosan modified by carboxylation with a degree of substitution of 0.6 to 0.8. Its molecular chain contains both cationic amino groups and anionic carboxyl groups. The pH is adjusted to an acidic range of 4.5 to 5.0 using acetic acid solution. At this point, the amino groups are protonated to positive NH3, causing the carboxymethyl chitosan to dissolve. The dissolution process involves the electrostatic repulsion between the positive charges on the molecular chain, causing the molecular chain to extend into… Add the sample to the aqueous phase and stir for 30 minutes until completely dissolved to form a transparent, viscous solution. Prepare modified bentonite separately by weighing 15 grams of sodium-based montmorillonite bentonite and mixing it with 3 grams of hexadecyltrimethylammonium bromide in an 80°C water bath for 2 hours. Hexadecyltrimethylammonium bromide is a cationic surfactant; its quaternary ammonium ions undergo ion exchange with sodium ions in the bentonite interlayer, allowing long carbon chains to insert into the bentonite interlayer, increasing the interlayer spacing from the original 1.2 nm to 3.8 nm. The interlayer spacing is determined by X-ray diffraction. X-rays are used to irradiate the sample. Diffraction peaks are generated. According to Bragg's equation, the interlayer spacing is calculated to be equal to the X-ray wavelength multiplied by the diffraction order divided by twice the sine of the diffraction angle. After the reaction, the supernatant is repeatedly washed with deionized water and anhydrous ethanol until no bromide ions are present. The bromide ion detection method involves adding silver nitrate solution to the supernatant; if a white precipitate appears, it indicates residual bromide ions, requiring further washing. After washing until the supernatant is clear, it is dried in an oven at 60°C to constant weight to obtain modified bentonite. The modified bentonite is then added to a carboxymethyl chitosan solution and stirred at high speed (800 rpm). The bentonite aggregates were dispersed by ultrasonication for 20 minutes under the following conditions: ultrasonic frequency 40 kHz, power 200 watts. The microjets and shock waves generated by ultrasonic cavitation broke up the bentonite aggregates. After dispersion, the surface potential was measured to be -15 to -20 mV by a Zeta potential analyzer. Then, the pH value was adjusted to a neutral range of 6.8 to 7.2. At this time, the amino groups of carboxymethyl chitosan were deprotonated and the carboxyl groups were dissociated. The molecular chains exhibited a zwitterionic state in which positively charged amino groups and negatively charged carboxyl groups coexisted, resulting in a mixed solution of carboxymethyl chitosan stabilizer.Next, a multi-component premixing process was performed. 600 ml of the chelated nutrient solution prepared in step one, 200 ml of the nano-chelated particle suspension prepared in step two, and 50 g of the three-layer gradient release microcapsules prepared in step three were added sequentially to the carboxymethyl chitosan stabilizer mixture at a mass ratio of 85:15. The order of addition was as follows: first, the chelated nutrient solution was added and stirred for 5 minutes to ensure thorough mixing with the carboxymethyl chitosan. The cationic amino groups on the carboxymethyl chitosan molecular chain combine with the negative charge on the surface of the metal chelate in the chelated nutrient solution through electrostatic interaction. Then, the nano-chelated particle suspension was added and stirred for 5 minutes. The negative charge layer of polyglutamic acid on the surface of the nanoparticles also combines with the cationic amino groups of the carboxymethyl chitosan. Ionic amino groups are combined, and finally, three-layer gradient release microcapsules are added and stirred for 5 minutes. The carboxyl groups at the end of the PLGA coating layer on the surface of the microcapsules are combined with carboxymethyl chitosan through hydrogen bonding. Premixing is carried out at a speed of 500 rpm for a total of 15 minutes. The premixing speed should be lower than the high-speed shear speed to avoid damaging the microcapsule structure. The viscosity of the system after premixing is measured by a rotational viscometer. The rotor is immersed in the slurry and rotated at a set speed. The viscosity is calculated based on the torque resistance experienced by the rotor. The viscosity value reflects the fluidity of the slurry. If the viscosity is too low, granulation will be difficult; if the viscosity is too high, spraying will be unsmooth. The amount of carboxymethyl chitosan is adjusted to control the viscosity within a suitable range to obtain a composite mixed slurry. Wet granulation was performed again to prepare a hydroxypropyl methylcellulose binder solution. Hydroxypropyl methylcellulose is a non-ionic, water-soluble polymer of cellulose modified by hydroxypropyl and methyl etherification. A viscosity specification of E5 indicates a 2% aqueous solution viscosity of 4 to 6 mPa·s. 8 grams of this solution were weighed and dissolved in 100 ml of distilled water. The composite slurry was then fed into a high-speed mixing granulator. The granulator consisted of a high-speed rotating impeller and a fixed granulation pot. The impeller speed was set to 1200 rpm. The binder solution was sprayed into the granulation pot through an atomizing nozzle at a spray rate of 4 ml / min and an atomization pressure of 0.25 MPa. The atomization pressure atomizes the adhesive solution into tiny droplets with a diameter of 50 to 100 micrometers. These droplets are sprayed onto the slurry surface to form liquid bridges. Liquid bridges are bridge-like structures that connect particles through the surface tension of the liquid. Under the mechanical shear force generated by high-speed stirring, the slurry agglomerates into spherical particles. The particle growth mechanism includes liquid bridge bonding that causes small particles to agglomerate into large particles, and adhesive curing that stabilizes the particle structure. The granulation time is 12 minutes. During the granulation process, the particle size gradually increases. The granulation endpoint is determined by sampling and observing the particle morphology. When the particle surface is smooth and the particle size distribution is concentrated, the spraying is stopped, and wet-granulated particles are obtained.Finally, the particles are screened and graded. The wet-granulated particles are fed into a vibrating screen, which has two layers of screens. The upper layer has a pore size of 3.5 mm and the lower layer has a pore size of 2.0 mm. The vibration frequency is 50 Hz and the amplitude is 5 mm. Under the action of vibration, the particles jump forward on the screen surface. Particles with a diameter greater than 3.5 mm remain on the upper screen surface, particles with a diameter of 2.0 to 3.5 mm pass through the upper screen and remain on the lower screen surface, and particles with a diameter less than 2.0 mm fall into the bottom collection tray after passing through both screens. The qualified particles with a diameter of 2.0 to 3.5 mm on the lower screen surface are collected. The qualified particle size is calculated by weighing, which is equal to the mass of qualified particles divided by the total mass of particles. The qualified particle size reflects the control level of the granulation process. Composite particles are obtained. The internal structure of the composite particles is that chelated nutrient solution and nano-chelated particles are evenly distributed in a carboxymethyl chitosan-modified bentonite matrix, and three-layer gradient release microcapsules are embedded in the core of the particles.

[0029] In one specific embodiment, carboxymethyl chitosan is dissolved in deionized water and modified bentonite is added and stirred to disperse, thereby obtaining a carboxymethyl chitosan stabilizer mixture, comprising: Carboxymethyl chitosan was added to deionized water and the pH was adjusted to the acidic range with acetic acid solution to protonate the amino groups and promote dissolution, thus obtaining a carboxymethyl chitosan solution. Sodium-based montmorillonite bentonite was subjected to an organic modification reaction with hexadecyltrimethylammonium bromide at a set temperature, followed by washing and drying to obtain modified bentonite. Modified bentonite was added to a carboxymethyl chitosan solution and ultrasonically dispersed under high-speed stirring until the interlayer spacing increased to obtain a bentonite dispersion. The surface potential distribution of the bentonite dispersion was measured using a Zeta potential analyzer, and the pH was adjusted to a neutral range to deprotonate the amino groups of carboxymethyl chitosan and dissociate the carboxyl groups to form zwitterionic states, thus obtaining a carboxymethyl chitosan stabilizer mixture.

[0030] Specifically, the key to preparing the carboxymethyl chitosan stabilizer mixture lies in four continuous processes: pH-controlled dissolution of carboxymethyl chitosan, organic modification of bentonite, ultrasonic dispersion, and the formation of amphoteric states. First, 25 grams of carboxymethyl chitosan are weighed and added to 200 ml of deionized water. Carboxymethyl chitosan is a derivative of chitosan whose hydroxyl groups are replaced by carboxymethyl groups, with a degree of substitution of 0.6 to 0.8. The degree of substitution is defined as the number of hydroxyl groups replaced by carboxymethyl groups per 100 glucosamine units. After substitution, both amino and carboxyl functional groups exist on the molecular chain. The pH value is adjusted to an acidic range of 4.5 to 5.0 by adding acetic acid solution dropwise. The principle of pH adjustment is that acetic acid ionizes in water to produce hydrogen ions, which react with the amino groups on the carboxymethyl chitosan molecular chain. The amino group is protonated to NH3, which increases the positive charge density on the molecular chain. The electrostatic repulsion between the positive charges causes the molecular chain to stretch from a coiled state to an extended chain state. The extended chain forms a hydration layer with water molecules through hydrogen bonding, thus achieving dissolution. The dissolution process is monitored by transmittance. 1 ml of sample is placed in a cuvette and the transmittance at a wavelength of 600 nm is measured using a spectrophotometer. The transmittance gradually increases from less than 10% in the initial turbid state. After stirring for 30 minutes, the transmittance reaches more than 95%, indicating complete dissolution, and a carboxymethyl chitosan solution is obtained.Next, modified bentonite was prepared. 15 grams of sodium-based montmorillonite bentonite was weighed. Montmorillonite is a 2:1 layered silicate mineral composed of two layers of silicon-oxygen tetrahedra sandwiching one layer of aluminum-oxygen octahedra. Sodium ions in the interlayer compensate for the negative charge of the layers, and the interlayer spacing is approximately 1.2 nanometers in its natural state. 3 grams of hexadecyltrimethylammonium bromide was also weighed. The hexadecyltrimethylammonium bromide molecule consists of a positively charged quaternary ammonium head group and a sixteen-carbon hydrophobic alkyl chain. The bentonite and hexadecyltrimethylammonium bromide were mixed in a beaker with 150 ml of deionized water and stirred in an 80°C water bath for 2 hours. The reaction process involved ion exchange between the quaternary ammonium ions of hexadecyltrimethylammonium bromide and the sodium ions in the bentonite interlayer. The driving force for this ion exchange was the electrostatic attraction between the quaternary ammonium ions of hexadecyltrimethylammonium bromide and the negative charge of the layers, which was greater than the attraction of the sodium ions. After the exchange, the long carbon chain inserted into the interlayer to widen the interlayer spacing. The interlayer spacing was then detected using X-ray diffraction. To investigate the interlayer spacing variation, a small sample was prepared into a powder tablet. X-ray irradiation of the sample produced diffraction. According to Bragg's equation, the interlayer spacing equals the X-ray wavelength divided by twice the sine of the diffraction angle and then multiplied by the diffraction order. Unmodified bentonite showed a diffraction peak at a diffraction angle of 7.2 degrees, corresponding to an interlayer spacing of 1.2 nanometers. After modification, the diffraction peak shifted to 2.3 degrees, corresponding to an interlayer spacing of 3.8 nanometers, representing a 3.2-fold increase in interlayer spacing. After the reaction was completed, the sample was washed with deionized water to remove unreacted hexadecyltrimethylammonium bromide and sodium bromide generated in the reaction. The washing procedure involved adding water, stirring, allowing the sample to settle, discarding the supernatant, and repeating the process five times. The washing endpoint was determined using the silver nitrate detection method. 1 ml of the supernatant was added to silver nitrate solution. If a white silver chloride precipitate appeared, it indicated the presence of residual bromide ions, requiring continued washing. After washing until no precipitate appeared when silver nitrate was added to the supernatant, the sample was dried in a 60°C oven to constant weight. Constant weight was determined when the difference between two consecutive weighings was less than 0.01 grams, yielding modified bentonite. 15 grams of modified bentonite were added to a carboxymethyl chitosan solution again. Ultrasonic treatment was applied simultaneously under high-speed stirring (800 rpm). The ultrasonic generator had a frequency of 40 kHz and a power of 200 watts. The ultrasonic waves propagated in the liquid, generating alternating pressure waves. Vacuum bubbles formed inside the liquid in the negative pressure zone. These bubbles instantly closed in the positive pressure zone, generating localized high-temperature and high-pressure shock waves. These shock waves dispersed the bentonite aggregates. Simultaneously, the shear force generated by high-speed stirring further dispersed the bentonite. After ultrasonic dispersion for 20 minutes, samples were taken and the particle size distribution was measured using a laser particle size analyzer. Laser irradiation of the suspension produced scattering of light from the particles. Larger particles had smaller scattering angles, while smaller particles had larger scattering angles. The instrument calculated the particle size distribution by analyzing the intensity distribution of scattered light from multiple angles. The median particle size of the modified bentonite decreased from 15 micrometers before dispersion to 0.8 micrometers after dispersion. This reduction in particle size indicates that the aggregates were broken up, resulting in a bentonite dispersion.Finally, the surface potential distribution of the bentonite dispersion was determined using a Zeta potential analyzer. One milliliter of the bentonite dispersion was diluted to a standard concentration and injected into the sample cell of the Zeta potential analyzer. An electric field was applied across the sample, causing charged particles to move within the field. Laser irradiation of the moving particles generated a Doppler frequency shift. The instrument calculated the particle electrophoretic mobility by measuring the frequency shift. The electrophoretic mobility is directly proportional to the Zeta potential of the particle surface. The measured Zeta potential was -15 to -20 mV. The negative potential originated from the negative charge on the modified bentonite layers. The pH was then adjusted dropwise with sodium hydroxide solution to a neutral range of 6.8 to 7.2. The increase in pH caused two changes in carboxymethyl chitosan: first, the amino group deprotonated from positive NH3 to negative NH2, reducing the positive charge on the molecular chain; second, the carboxyl group dissociated from negative COOH to negative COO. Increasing the negative charge of the molecular chain results in two simultaneous changes, causing the carboxymethyl chitosan molecular chain to exhibit an amphoteric state where positive amino charges and negative carboxyl charges coexist. In this amphoteric state, the positive amino charges are attracted to the negative charges on the surface of modified bentonite through electrostatic attraction, while the negative carboxyl charges are attracted to the negative charges on the surface of subsequently added nano-chelate particles through electrostatic repulsion. The positive amino charges are bonded to the PLGA carboxyl groups on the surface of the three-layer gradient release microcapsules through hydrogen bonding. The amphoteric state of carboxymethyl chitosan acts as a "molecular bridge" between different components, resulting in a carboxymethyl chitosan stabilizer mixture. In this mixture, modified bentonite is dispersed as a nanocarrier in the carboxymethyl chitosan solution. The large specific surface area of ​​bentonite (280 m² / g as determined by the nitrogen adsorption BET method) adsorbs and fixes chelated nutrients. The amphoteric structure of carboxymethyl chitosan achieves dynamic stability of different components.

[0031] In one specific embodiment, step S5 includes: Hydroxypropyl methylcellulose, polyethylene glycol and talc are dissolved in distilled water to form a rapid disintegration film coating solution, which is then sprayed onto the surface of composite particles at a set temperature using a fluidized bed coating machine to obtain rapid disintegration film coated particles. A methacrylic acid copolymer, triacetyl ester, and titanium dioxide were dissolved in an ethanol-water mixed solvent to form an enteric coating solution. The solution was sprayed onto the surface of rapid-disintegrating membrane-coated particles under reduced temperature conditions, and the membrane density was detected by atomic force microscopy to obtain enteric coating particles. Chitosan was cross-linked with glutaraldehyde and then mixed with sodium alginate and sodium carboxymethyl cellulose and dissolved in acetic acid solution to form an enzyme-responsive membrane coating solution. After being sprayed onto the surface of enteric membrane coated particles, the chitosan was neutralized by sodium hydroxide atomization solution to allow the chitosan to be deposited in situ, thus obtaining three-layer coated particles. The three-layer coated particles are dried in a vacuum drying oven and then sprayed with an antioxidant protective liquid of ascorbic acid and tocopherol, as well as a surfactant liquid of lecithin and polysorbate. After that, they are extruded and cured by rollers to obtain the target growth agent.

[0032] Specifically, to prepare the rapid-disintegrating film coating, 8 grams of hydroxypropyl methylcellulose (HMCMC) were weighed as the film-forming matrix. HMCMC specification E5 indicates a 2% aqueous solution with a viscosity of 4 to 6 mPa·s. Its molecular chain has a methyl substitution degree of 1.5 to 1.9 and a hydroxypropoxy substitution degree of 0.13 to 0.32. The hydroxypropyl and methyl substitutions enhance the water solubility of cellulose. 2 grams of polyethylene glycol 400 (molecular weight 380 to 420 Daltons) were weighed as a plasticizer. The plasticizer inserts between polymer chains, increasing chain segment mobility and reducing film brittleness. 1 gram of talc was weighed as a flow aid. The talc's layered structure reduces interparticle friction and improves flowability. All three were dissolved in 100 ml of distilled water and stirred until completely dissolved to form the rapid-disintegrating film coating solution. The composite particles prepared in step four were then fed into a fluidized bed coating machine. The fluidized bed works by blowing hot air into the bottom to suspend and fluidize the particles. The inlet air temperature was set at 55℃, the outlet air temperature at 42℃, and the temperature difference at 13℃. The temperature (°C) indicates that heat is used for liquid evaporation. The relative humidity inside the bed is controlled between 35% and 45%. If the humidity is too high, the film layer will stick; if the humidity is too low, atomization will be poor. The coating liquid is sprayed through a dual-fluid spray gun at an atomization pressure of 0.25 MPa and a spraying speed of 4 ml per minute. The atomization pressure breaks the liquid into droplets with a diameter of 50 to 100 micrometers. The droplets are sprayed onto the surface of the fluidized particles and spread into a liquid film. After the hot air evaporates the moisture, the film-forming material is deposited on the particle surface. The coating time is 18 minutes. During the coating process, samples are taken every 5 minutes to observe the film formation under a microscope. The film thickness is calculated by the weight gain rate. The weight of the film layer is obtained by subtracting the weight of the particles before coating from the total weight of the particles after coating. The weight gain rate is 3.5% when the weight of the film layer is divided by the weight of the particles before coating and multiplied by 100%. The film thickness is equal to the particle radius multiplied by the weight gain rate, divided by 100%, and then divided by the density of the film-forming material. The film thickness is measured to be 20 to 30 micrometers, and the rapidly disintegrating film-coated particles are obtained.Next, a pH-sensitive enteric-coated membrane was prepared. 12 grams of methacrylic acid copolymer (trade name Eudragit L100) was weighed out; this copolymer is polymerized from methacrylic acid and methyl methacrylate in a 1:1 molar ratio. The carboxyl groups on the molecular chain are protonated to negative COOH at pH less than 6.0, becoming insoluble, and deprotonated to negative COO at pH greater than 6.5, becoming soluble. 3 grams of triacetin were weighed out as a plasticizer, and 0.5 grams of titanium dioxide were weighed out as a light-blocking agent to prevent photodegradation of the internal active ingredients. These three were dissolved in 120 ml of an ethanol-water mixture (volume ratio 7:3) to form the enteric-coated membrane coating solution. Due to the rapid evaporation of ethanol, the fluidized bed temperature needed to be lowered to 48°C to prevent instantaneous evaporation and resulting membrane roughness. The solution was sprayed onto the surface of the rapidly disintegrating membrane particles at a spray rate of 5 ml / min for 25 minutes. The weight increase after coating was [not specified]. A 5.8% addition rate corresponds to a film thickness of 40 to 60 micrometers. The film density was detected using an atomic force microscope (AFM). The working principle of the AFM is that the interatomic forces between the probe tip and the sample surface cause a slight deflection of the cantilever. Laser illumination of the cantilever is reflected to a photodiode detector, and the detector output signal reflects the surface morphology. The tapping mode was selected for scanning to avoid damaging the film with the probe tip. The scanning range was 10 micrometers by 10 micrometers. After scanning, a three-dimensional morphology image was obtained. The surface roughness was calculated using image processing software. The arithmetic mean of the roughness, Ra, is equal to the arithmetic mean of the absolute values ​​of all height deviations in the measurement area. The measured Ra value was 8.5 nanometers. A roughness of less than 10 nanometers indicates that the film is dense and smooth, yielding enteric-coated particles. To prepare the enzyme-responsive membrane again, 15 grams of chitosan were dissolved in acetic acid solution (2% concentration), and 0.5 grams of glutaraldehyde were added for cross-linking. The aldehyde groups at both ends of the glutaraldehyde molecule reacted with the amino groups on the chitosan molecular chain through a Schiff base reaction to form imine bonds for cross-linking. The degree of cross-linking was defined as the percentage of amino groups participating in cross-linking to the total number of amino groups. The degree of cross-linking was determined by the ninhydrin colorimetric method. Uncross-linked amino groups reacted with ninhydrin to produce a blue-purple color. The content of uncross-linked amino groups was calculated by absorbance. The degree of cross-linking equals 1 minus the content of uncross-linked amino groups divided by the total amino group content. The measured degree of cross-linking was 25%. After cross-linking, the chitosan did not dissolve at neutral pH. Sodium alginate was prepared separately. 2 grams of sodium carboxymethyl cellulose (CCMC) were dissolved in an acetic acid solution. The CCMC had a degree of substitution of 0.7 and a degree of polymerization of 300 to 500. Cross-linked chitosan and sodium alginate were mixed to form an enzyme-responsive membrane coating solution. The solution was sprayed onto the surface of the enteric membrane-coated particles at a spraying rate of 3 ml per minute. During the spraying process, sodium hydroxide atomized solution (concentration of 5 g per liter) was sprayed simultaneously through another nozzle. The sodium hydroxide neutralized the acetic acid, raising the pH. The amino groups of chitosan were deprotonated and deposited in situ on the particle surface to form an insoluble membrane layer. The coating time was 30 minutes, and the weight gain rate was 8.2%, corresponding to a membrane thickness of 60 to 90 micrometers, resulting in three-layer coated particles.Finally, the three-layer coated granules were evenly spread on a stainless steel tray with a thickness not exceeding 3 cm, and placed in a vacuum drying oven at a vacuum degree of -0.08 MPa and a temperature of 45°C. The vacuum negative pressure lowers the boiling point of water and accelerates evaporation. Drying was carried out for 6 hours, turning the granules every 2 hours. The moisture content was measured using a Karl Fischer moisture analyzer. A 0.5 g sample was added to the Karl Fischer reagent. The amount of iodine consumed in the reaction of iodine with water in the reagent is directly proportional to the water content. The moisture content was calculated to be reduced to 2.3% by potentiometric titration to determine the iodine consumption. Antioxidant preparations were then prepared. A protective solution was prepared by dissolving 3 g of ascorbic acid, 2 g of tocopherol, 1 g of propyl gallate, and 0.5 g of ethoxyquinoline in 100 ml of anhydrous ethanol. This solution was then sprayed onto the surface of dried particles through an ultrafine atomizing nozzle at a droplet diameter of less than 50 micrometers and a spraying rate of 1.5 ml / min. The particles were then dried in a fluidized bed at 45°C for 15 minutes to form a transparent protective film with a thickness of 5 to 10 micrometers. A surfactant solution was also prepared by adding 5 g of lecithin, 3 g of dehydrated sorbitan monostearate (HLB value 4.7), and 80 g of polysorbate. 2 grams (HLB value 15) were compounded in a 3:2 ratio to form an HLB value 8.5 emulsion system. The HLB value is the hydrophilic-lipophilic balance value, characterizing the hydrophilicity and lipophilicity of surfactants. A higher HLB value indicates stronger hydrophilicity. The compounded HLB value is equal to the sum of the HLB values ​​of each component multiplied by their mass fraction. This solution was dissolved in 120 ml of isopropanol-water (volume ratio 1:1) and sprayed onto the surface of the granules at a rate of 2 ml / min. After drying at 40°C for 20 minutes, the surface wettability was measured using a contact angle meter. The contact angle meter was used to drop water onto the surface of the compressed granules, and the image was captured using a side-view camera. The contact angle between water droplets and solid surfaces decreased from 85 degrees in untreated samples to 32 degrees. A smaller contact angle indicates better wettability. The treated granules were fed into a roller extrusion granulator with a roller pressure of 15 MPa, a roller speed of 80 rpm, and a roller gap of 2.5 mm. Under the extrusion of the rollers, the internal voids of the granules were compressed, and the bulk density increased from 0.68 g / cm³ to 0.92 g / cm³. The compressive strength of a single particle was measured to be 25 N using a hardness tester. Qualified granules with a particle size of 2.0 to 3.0 mm were collected by vibrating sieve grading to obtain rhizosphere nutrient fortification and signal-induced growth agent.

[0033] In one specific embodiment, the three-layer coated particles are dried in a vacuum drying oven and then sprayed with an antioxidant protective solution of ascorbic acid and tocopherol, and a surfactant solution of lecithin and polysorbate, followed by roller extrusion curing to obtain the target growth agent, comprising: The three-layer coated particles are evenly spread in a tray and sent into a vacuum drying oven to dry to the target moisture content under the set vacuum degree and temperature to obtain dried coated particles. Ascorbic acid, tocopherol, propyl gallate and ethoxyquinoline were dissolved in anhydrous ethanol to form an antioxidant protective solution, which was then sprayed onto the surface of dried coated particles through an ultrafine atomizing nozzle and dried in a fluidized bed to obtain antioxidant-treated particles. Lecithin, dehydrated sorbitan monostearate, and polysorbate were compounded and dissolved in an isopropanol-water mixed solvent to form a surfactant solution. The solution was sprayed onto the surface of the antioxidant-treated particles and dried. The surface wettability was then tested using a contact angle meter to obtain surface-active modified particles. The surface-modified particles are fed into a double-roller extrusion granulator and extruded under a set roller pressure. After the compressive strength of the particles is tested by a hardness tester, the qualified particles are collected by vibrating sieve to obtain the target growth agent.

[0034] Specifically, the three-layer coated granules are evenly spread in a stainless steel tray, with a thickness not exceeding 3 cm. This thickness limit ensures uniform drying. The granules are then placed in a vacuum drying oven with a vacuum level set to -0.08 MPa. Vacuum level is defined as the difference between absolute pressure and atmospheric pressure; -0.08 MPa means the absolute pressure inside the oven is 0.08 MPa lower than standard atmospheric pressure. The vacuum lowers the boiling point of water. Water boils at 100°C at normal pressure, but at -0.08 MPa, the boiling point drops to approximately 60°C. The temperature is set at 45°C, which, although lower than the boiling point at normal pressure, is sufficient to evaporate the water under vacuum. The drying time is 6 hours, with the granules turned every 2 hours to ensure even exposure to the heat source. The moisture content is measured using a Karl Fischer moisture analyzer. The Karl Fischer method works by the reaction of iodine with water, consuming iodine. The amount of iodine is directly proportional to the water content. After grinding 0.5 g of the sample, Karl Fischer reagent is added. Iodine in the reagent reacts with water through a redox reaction to produce hydroiodic acid and sulfur dioxide. The reaction equation is: iodine + sulfur dioxide + water to produce hydroiodic acid and sulfur trioxide. The amount of iodine consumed is determined by potentiometric titration. Platinum electrode and reference electrode are inserted into the sample in the potentiometric titrator. As iodine is consumed by the reaction with water, the solution potential jumps abruptly. The water content is calculated based on the volume of titrant corresponding to the potential jump point. The mass fraction of water content is equal to the volume of titrant multiplied by the titrant concentration multiplied by the molecular weight of water divided by the sample mass. The water content is measured to be reduced to 2.3%. The mass loss rate is equal to the mass before drying minus the mass after drying and then divided by the mass before drying. The mass loss rate is 12%, and the dried coated particles are obtained. Next, an antioxidant protective solution was prepared. 3 grams of L-ascorbic acid were weighed out. The enediol group in the L-ascorbic acid molecule has strong reducing properties and scavenges free radicals. 2 grams of tocopherol were weighed out. The phenolic hydroxyl group in the tocopherol molecule has a strong electron-donating ability and captures lipid peroxidation free radicals. 1 gram of propyl gallate was weighed out. The three ortho-hydroxyl groups in the propyl gallate molecule work synergistically to enhance antioxidant capacity. 0.5 grams of ethoxyquinoline were weighed out. The quinoline ring structure of ethoxyquinoline blocks the oxidation chain reaction. The four antioxidants were dissolved in 100 ml of anhydrous ethanol to form the antioxidant protective solution. This solution was then sprayed onto the surface of the dried coated particles through an ultrafine atomizing nozzle. The nozzle orifice diameter is less than 50 micrometers, producing droplets with a diameter of less than 50 micrometers. The spraying rate is 1.5 ml / min. During the spraying process, the particles are kept in a fluidized state in the fluidized bed. The droplets spread into a liquid film upon contact with the particle surface. The particles are dried in the fluidized bed at 45°C for 15 minutes. Ethanol, with a boiling point of 78°C, gradually evaporates at 45°C. The evaporation rate is affected by temperature and airflow speed. After complete evaporation, the antioxidant is deposited on the particle surface, forming a transparent protective film with a thickness of 5 to 10 micrometers. The film thickness is determined by cross-sectional observation using a scanning electron microscope (SEM). The SEM scans the sample surface with an electron beam, and the secondary electron signal reflects the surface morphology, thus obtaining the antioxidant-treated particles.Prepare the surfactant solution again. Weigh 5 grams of lecithin. Lecithin is a natural amphoteric surfactant containing both a hydrophilic phosphate head group and a hydrophobic fatty acid tail chain. Weigh 3 grams of sorbitan monostearate. Span 60 has a hydrophilic-lipophilic balance (HLB) of 4.7. The HLB value is defined as the percentage of the hydrophilic group's molecular weight in the surfactant molecule multiplied by 20. HLB values ​​of 0 to 10 indicate lipophilicity, and 10 to 20 indicate hydrophilicity. Weigh 2 grams of polysorbate 80. Tween 80 has an HLB value of 15. Combine 3 grams of sorbitan monostearate with polysorbate 80. Two grams were compounded in a 3:2 mass ratio. The HLB value of the compounded system was equal to the sum of the HLB values ​​of each component multiplied by their mass fractions. This was calculated as 4.7 multiplied by 3 divided by 5 plus 15 multiplied by 2 divided by 5, which equals 8.82, approximately 8.5. An HLB value of 8.5 indicates that the compounded system has good oil-water interfacial activity and is suitable as a wetting agent. Lecithin, dehydrated sorbitan monostearate, and polysorbate were dissolved in 120 ml of isopropanol-water mixed solvent (volume ratio 1:1). Isopropanol served as a co-solvent to aid in the dissolution of lecithin. The solution was sprayed onto the surface of the antioxidant-treated particles at a spraying rate of 2 ml per minute. The solvent was evaporated by fluidized bed drying at 40°C for 20 minutes. The surfactant formed a directional arrangement on the particle surface. The hydrophobic ends were adsorbed onto the particle coating layer through the hydrophobic interaction of the alkyl chains, while the hydrophilic ends were polar. With the group facing outwards, the surface wettability was tested using a contact angle meter. The working principle of the contact angle meter is to drop a standard volume of water onto the surface of the granule tablet, and then use a side-view camera to capture the angle formed at the contact point between the water droplet and the solid surface. The contact angle is defined as the angle between the droplet and the tangent of the solid surface. The smaller the contact angle, the stronger the hydrophilicity and the better the wettability of the solid surface. The measurement operation involves pressing the granules into tablets with a flat surface in a tablet press, and then adding 2 microliters of deionized water to the surface of the tablet using a micro-syringe. After the water droplet lands on the surface, the shape of the water droplet is captured by a high-speed camera. Image processing software fits the water droplet contour curve and calculates the contact angle. The contact angle of the untreated granules is 85 degrees, while the contact angle after surface-active modification decreases to 32 degrees. The decrease in contact angle indicates a shortened wetting and disintegration time, resulting in surface-active modified granules.Finally, the surface-modified particles were fed into a double-roller extrusion granulator. This granulator consists of two counter-rotating rollers. The roller pressure was set to 15 MPa, applied via a hydraulic system. The roller speed was set to 80 rpm, and the roller gap was set to 2.5 mm. As the particles passed through the gap, they were compressed. This compression increased the particle bulk density, defined as the mass of particles per unit volume. Bulk density was determined using the graduated cylinder method. A fixed mass of particles was poured into a graduated cylinder, vibrated, and the volume was read. Bulk density equals the particle mass divided by the volume. Before extrusion, the bulk density was 0.68 g / cm³, and after extrusion, it was 0.92 g / cm³. The increase in bulk density indicates improved particle compaction. The compressive strength of a single particle was then tested using a hardness tester. The hardness tester's working principle is based on probing... The probe presses down on the particles at a constant speed until the particles break. The force applied by the probe at the moment of breakage is recorded as the compressive strength. The measured compressive strength is 25 Newtons. The compressive strength is related to the density of the internal structure of the particles and the bonding strength between the components. The higher the density and the tighter the bonding, the greater the compressive strength. After compression, the particles are put into a vibrating screen, which consists of two layers of screens: an upper layer with a 3.5 mm aperture and a lower layer with a 2.0 mm aperture. The vibration frequency is 50 Hz and the amplitude is 5 mm. The particles jump forward under the vibration. Particles with a diameter greater than 3.5 mm remain in the upper layer, particles with a diameter between 2.0 and 3.5 mm remain in the lower layer, and particles with a diameter less than 2.0 mm fall to the bottom. The qualified particles on the lower screen are collected, and the qualified particle size rate is calculated by weighing. The qualified particle size rate is equal to the mass of qualified particles divided by the total mass of particles multiplied by 100%. The rhizosphere nutrient fortification and signal-induced growth agent is obtained.

[0035] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing rhizosphere nutrient enhancement and signal-induced growth agents, characterized in that, The method includes: Step S1: Potassium nitrate, potassium dihydrogen phosphate, and magnesium sulfate are chelated with EDTA-citric acid double chelating agent under alkaline conditions, and then a dynamic chelation equilibrium is formed by pH adjustment and vacuum concentration to obtain chelated nutrient solution. Step S2: Ferrous sulfate, zinc sulfate, manganese sulfate, boric acid and sodium molybdate are chelated with amino acids, then polyglutamic acid is added for surface modification and high-speed shear emulsification to obtain a suspension of nano-chelated particles. Step S3: Oligosaccharides are encapsulated with cyclodextrin to form an immediate-release layer, hormone signaling molecules are encapsulated with calcium alginate gel to form a sustained-release layer, and then coated with PLGA solution to form a controlled-release layer, thus obtaining a three-layer gradient release microcapsule; Step S4: The chelated nutrient solution, the nano-chelated particle suspension, and the three-layer gradient release microcapsules are added to a carboxymethyl chitosan solution, mixed, and wet-granulated to obtain composite particles; Step S5: The composite particles are sequentially coated with a rapid-disintegration membrane, a pH-sensitive enteric membrane, and a cellulase-responsive membrane, and then dried and stabilized to obtain the target growth agent.

2. The method for preparing rhizosphere nutrient enhancement and signal-induced growth agent according to claim 1, characterized in that, Step S1 includes: Potassium nitrate, potassium dihydrogen phosphate and magnesium sulfate were dissolved in deionized water and stirred at a constant temperature to obtain an aqueous solution of nutrients. Add disodium EDTA dropwise to the aqueous solution of the nutrient elements at a set mass ratio and simultaneously adjust the pH value to the alkaline range to obtain the EDTA chelation reaction solution; The pH change rate of the EDTA chelation reaction solution was monitored by pH titration curve. When the pH change rate was lower than the set threshold, citric acid was added and the pH value was kept stable to obtain a double chelation reaction solution. The double chelate reaction solution is heated and concentrated under vacuum to a set ratio of its initial volume to obtain a chelated nutrient solution.

3. The method for preparing rhizosphere nutrient enhancement and signal-induced growth agent according to claim 1, characterized in that, Step S2 includes: Ferrous sulfate, zinc sulfate, manganese sulfate, boric acid, and sodium molybdate are dissolved in deionized water to obtain an aqueous solution of trace elements. Add a compound amino acid chelating agent of glycine and glutamic acid to the aqueous solution of trace elements and adjust the pH value to the alkaline range to carry out the chelation reaction to obtain an amino acid chelated solution. Polyglutamic acid was added to the amino acid chelate solution and the pH was adjusted to a neutral range to dissociate the carboxyl groups of the polyglutamic acid side chain and form a negatively charged coating layer, thereby obtaining a surface-modified chelate solution. The surface-modified chelate was sheared at a set speed using a high-speed shear emulsifier, and the particle size distribution was detected to the nanoscale range using a dynamic light scattering instrument to obtain a nano-chelate particle suspension.

4. The method for preparing rhizosphere nutrient enhancement and signal-induced growth agent according to claim 1, characterized in that, Step S3 includes: Chitosan oligosaccharide and alginate oligosaccharide were dissolved in acetate buffer, and then β-cyclodextrin aqueous solution was added. The mixture was stirred at a set temperature to induce an inclusion reaction. After cooling, crystals were precipitated and filtered and dried to obtain oligosaccharide inclusion complex immediate-release particles. Indoleacetic acid, benzylaminopurine and gibberellin were dissolved in anhydrous ethanol to form a hormone mixture, which was then mixed with sodium alginate solution and injected into calcium chloride solution via an injection pump for cross-linking and gelation to obtain hormone-encapsulated gel microspheres. Polylactic acid-glycolic acid copolymer was dissolved in dichloromethane to form a PLGA organic phase. The hormone-encapsulated gel microspheres were added to the PLGA organic phase and polyvinyl alcohol aqueous solution was added. The mixture was emulsified in a high-speed homogenizer to form a complex emulsion system. The system was then transferred to distilled water and stirred to evaporate the organic solvent, allowing PLGA to be deposited and solidified on the surface of the microspheres to obtain PLGA-coated microspheres. The oligosaccharide inclusion complex rapid-release particles are mixed with the PLGA-coated microspheres at a set mass ratio to obtain three-layer gradient release microcapsules.

5. The method for preparing rhizosphere nutrient enhancement and signal-induced growth agent according to claim 1, characterized in that, Step S4 includes: Carboxymethyl chitosan was dissolved in deionized water and modified bentonite was added and stirred to disperse, thus obtaining a carboxymethyl chitosan stabilizer mixture. The chelated nutrient solution, the nano-chelated particle suspension and the three-layer gradient release microcapsules are sequentially added to the carboxymethyl chitosan stabilizer mixture at a set mass ratio and premixed at a set rotation speed to obtain a composite slurry. Hydroxypropyl methylcellulose binder solution is sprayed into the composite slurry through an atomizing nozzle and then sheared and granulated in a high-speed mixer to obtain wet-granulated particles. The wet-granulated particles are vibrated and screened, and particles within a set particle size range are collected to obtain composite particles.

6. The method for preparing rhizosphere nutrient enhancement and signal-induced growth agent according to claim 5, characterized in that, The process involves dissolving carboxymethyl chitosan in deionized water and adding modified bentonite, followed by stirring and dispersing to obtain a carboxymethyl chitosan stabilizer mixture, comprising: Carboxymethyl chitosan was added to deionized water and the pH was adjusted to the acidic range with acetic acid solution to protonate the amino groups and promote dissolution, thus obtaining a carboxymethyl chitosan solution. Sodium-based montmorillonite bentonite was subjected to an organic modification reaction with hexadecyltrimethylammonium bromide at a set temperature, followed by washing and drying to obtain modified bentonite. The modified bentonite was added to the carboxymethyl chitosan solution and ultrasonically dispersed under high-speed stirring until the interlayer spacing increased to obtain a bentonite dispersion. The surface potential distribution of the bentonite dispersion was measured using a Zeta potential analyzer, and the pH value was adjusted to a neutral range to deprotonate the amino groups of carboxymethyl chitosan and dissociate the carboxyl groups to form zwitterionic states, thereby obtaining a carboxymethyl chitosan stabilizer mixture.

7. The method for preparing rhizosphere nutrient enhancement and signal-induced growth agent according to claim 1, characterized in that, Step S5 includes: Hydroxypropyl methylcellulose, polyethylene glycol and talc are dissolved in distilled water to form a rapid disintegration film coating solution, which is then sprayed onto the surface of the composite particles using a fluidized bed coating machine at a set temperature to obtain rapid disintegration film coated particles. A methacrylic acid copolymer, triacetin, and titanium dioxide were dissolved in an ethanol-water mixed solvent to form an enteric coating solution. The solution was sprayed onto the surface of the rapidly disintegrating film-coated particles under reduced temperature conditions, and the film density was detected by atomic force microscopy to obtain enteric coating particles. Chitosan was cross-linked with glutaraldehyde and then mixed with sodium alginate and sodium carboxymethyl cellulose and dissolved in acetic acid solution to form an enzyme-responsive membrane coating solution. The solution was sprayed onto the surface of the enteric membrane coated particles and then neutralized by sodium hydroxide atomization solution to allow chitosan to be deposited in situ, thus obtaining three-layer coated particles. The three-layer coated particles are dried in a vacuum drying oven and then sprayed with an antioxidant protective liquid of ascorbic acid and tocopherol, as well as a surfactant liquid of lecithin and polysorbate, and then pressed and cured by roller extrusion to obtain the target growth agent.

8. The method for preparing rhizosphere nutrient enhancement and signal-induced growth agent according to claim 7, characterized in that, The process involves drying the three-layer coated particles in a vacuum drying oven, spraying them with an antioxidant protective solution of ascorbic acid and tocopherol, and a surfactant solution of lecithin and polysorbate, followed by roller extrusion curing to obtain the target growth agent, comprising: The three-layer coated particles are evenly spread in a tray and sent into a vacuum drying oven to dry to the target moisture content under a set vacuum degree and temperature to obtain dried coated particles. Ascorbic acid, tocopherol, propyl gallate and ethoxyquinoline are dissolved in anhydrous ethanol to form an antioxidant protective solution, which is then sprayed onto the surface of the dried coated particles through an ultrafine atomizing nozzle and dried in a fluidized bed to obtain antioxidant-treated particles. Lecithin, dehydrated sorbitan monostearate, and polysorbate were compounded and dissolved in an isopropanol-water mixed solvent to form a surfactant solution. The solution was sprayed onto the surface of the antioxidant-treated particles and dried. The surface wettability was then tested using a contact angle meter to obtain surface-active modified particles. The surface-active modified particles are fed into a double-roller extrusion granulator and extruded under a set roller pressure. After the compressive strength of the particles is tested by a hardness tester, the qualified particles are collected by vibratory sieving to obtain the target growth agent.

9. The method for preparing rhizosphere nutrient enhancement and signal-induced growth agent according to any one of claims 1-8, or the application of the rhizosphere nutrient enhancement and signal-induced growth agent obtained by the preparation method according to any one of claims 1-8 in agricultural planting.

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