Preparation method of water-soluble fertilizer rich in various active amino acids

Abstract

The invention relates to the technical field of agricultural fertilizer preparation, and discloses a preparation method of a water-soluble fertilizer rich in various active amino acids, which comprises the following steps: S1, preparing an amino acid solution: dissolving various free amino acids or polypeptides in a buffer solution to form an amino acid precursor liquid; s2, constructing a nutrition core layer: adding one or more types of soluble trace element salts and a gelation auxiliary agent into the amino acid precursor liquid to form gelatinous particles; s3, forming an intermediate response layer: coating the core particles with chitosan and phospholipid to form a bimolecular membrane structure. The stability of the particle structure is improved through low-temperature crosslinking and bi-component gelation, and quick response and continuous controlled release in a weak acid environment are realized by combining an intermediate response membrane and an outer controlled release shell layer; by adopting a structure-function integrated design, the suspension property and the dispersity are remarkably improved, and the multi-crop and multi-period precise fertilization requirements are met.

Description

Technical Field

[0001] The present invention relates to the technical field of agricultural fertilizer preparation, and specifically to a preparation method of water-soluble fertilizer rich in various active amino acids. Background Art

[0002] As a type of efficient liquid nutrient carrier emerging in recent years, amino acid-based water-soluble fertilizers show good application prospects in improving crop nutrient absorption efficiency, promoting root activity, and improving soil microecology. They are mainly prepared by hydrolyzing proteins in plant sources, animal sources, or industrial by-products into small molecular free amino acids, and then through processes such as concentration and formulation to form liquid or granular fertilizers, with characteristics such as strong water solubility, easy absorption, and high biological activity. Especially in the fields of protected agriculture, drip irrigation fertilization, and chelation of medium and trace elements, active amino acid water-soluble fertilizers are gradually becoming an important supplement and upgrading direction for traditional inorganic fertilizers.

[0003] Currently, commercially available amino acid water-soluble fertilizers are mainly based on single hydrolysis products, and common sources include by-product raw materials such as feather meal, animal viscera hydrolysates, or corn steep liquor. Although these sources have certain advantages in cost control, the obtained amino acid types are relatively single, and the content of some essential amino acids (such as tryptophan, lysine, threonine) is relatively low, restricting the nutritional coordination function of the product throughout the crop growth process. In addition, due to complex raw materials or imperfect production process control, some products are prone to residual unreacted macromolecular proteins or impurity salts, which not only affect water solubility but may also cause spray irrigation blockage or reaction precipitation with other nutrients.

[0004] In terms of preparation processes, existing technologies mostly use methods such as acid hydrolysis, alkali hydrolysis, or enzymatic hydrolysis to obtain amino acid solutions, and then form powder or concentrated liquid products through methods such as spray drying, freeze drying, or thermal concentration. However, in practical applications, there are several common problems: First, although the acid-base hydrolysis method is efficient, it causes great damage to thermosensitive amino acids and affects their biological activity; second, some enzymatic hydrolysis processes lack type matching and segmented control, resulting in unbalanced amino acid composition; third, the target components are not reasonably protected during the concentration or drying process, leading to serious loss of volatile or thermally degradable amino acids, thus affecting the final product quality and stability.

[0005] On the other hand, the stability of active components in amino acid fertilizers has also received extensive attention. Free amino acids have strong hydrophilicity and reactivity, and are prone to oxidation, cross-linking, or precipitation reactions in an aqueous solution environment, especially during high-temperature storage or complex nutrient mixing processes, and their content and biological effects will change. In addition, during transportation and storage, some amino acid water-soluble fertilizers exhibit phenomena such as precipitation, stratification, and color change, revealing problems such as insufficient stable protection of amino acids and imperfect system structure design in the preparation system. Summary of the Invention

[0006] In view of the deficiencies of the prior art, the present invention provides a method for preparing a water-soluble fertilizer rich in various active amino acids, which solves the problems of unbalanced amino acid types, unstable biological activity, and easy sedimentation and stratification during storage in existing amino acid water-soluble fertilizers.

[0007] To achieve the above objectives, the present invention is realized through the following technical solutions: A method for preparing a water-soluble fertilizer rich in various active amino acids, comprising the following steps: S1. Prepare an amino acid solution: Dissolve various free amino acids or polypeptides in a buffer solution to form a precursor amino acid solution; This step ensures the comprehensive nutrient supply of the final product at different stages of plant growth by reasonably matching essential and functional amino acids, and at the same time forms a stable precursor solution, providing a good dispersion environment for the uniform construction of the subsequent carrier structure. There are charge and hydrophilic group complementarities among various amino acids, which helps to stabilize the colloid system and improve the uniformity of the gel network in the subsequent reaction; S2. Construct a nutrient core layer: Add one or more types of soluble trace element salts and a gelation auxiliary agent to the precursor amino acid solution to form gel-like particles; This step constructs a nutrient core with a dense structure through the synergistic gelation effect of low-temperature-induced polyvinyl alcohol and polylactic acid. Polylactic acid provides a hydrophobic backbone, while polyvinyl alcohol endows it with hydrophilic flexible chain segments, forming a multi-point hydrogen bond and physical entanglement structure between the two. Under low-temperature conditions, the movement rate of the chain segments decreases, which is conducive to the uniform formation of cross-linking points, significantly improving the uniformity of the core particle size and the structural stability during long-term storage, and avoiding stratification and sedimentation caused by colloid swelling or depolymerization; S3. Form an intermediate response layer: Coating the core particles with chitosan and phospholipids to form a bimolecular membrane structure; The intermediate membrane layer formed in this step is a biomimetic membrane structure. Chitosan provides a positively charged backbone, and phospholipids are amphiphilic materials. The two self-assemble into a stable interfacial bilayer at a certain temperature condition, having strong pH responsiveness. When applied to the rhizosphere weak acid environment (pH≈5.5 - 6.0), chitosan can undergo protonation swelling, and at the same time, the phospholipid membrane has a structural loosening, opening the nutrient release channel, playing a "central control" role of "environmental sensing", which is the key response layer of the entire controlled release system; S4. Construct an outer controlled release layer: Further coating the bimolecular membrane structure particles with sodium alginate and sodium polyacrylate to form an outer shell; This outer shell as a controlled release layer has typical ion responsiveness. It is firmly combined based on the "egg box structure" of Ca²⁺ and sodium alginate, stable under neutral storage conditions, but when encountering the rhizosphere weak acid environment or an increase in ion concentration, the structure will gradually loosen, regulating the release rhythm of internal nutrients. Sodium polyacrylate enhances the flexibility and controllable permeability of the membrane layer, enabling the controlled release layer to have the "time - concentration synergistic response" ability on the basis of slow release; S5, pH adjustment and final formulation control: Adjust the pH of the coated particles, control the particle size, and prepare a water-soluble liquid or powder-type water-soluble fertilizer product containing uniformly dispersed coated particles; In this step, by adjusting the overall charge state of the system, the mutual repulsive force between particles is enhanced, effectively preventing colloid aggregation. At the same time, combined with physical particle size control technology, the dispersion uniformity and suspension stability of the system are ensured, so that the final product has good long-term storage performance and on-site use convenience.

[0008] Preferably, in the S1 step, the amino acids include at least five of glutamic acid, lysine, proline, valine, serine, and leucine, and the total mass of the amino acids accounts for 15% - 30% of the final system.

[0009] Preferably, the trace element salts in the S2 step are selected from one or more of zinc sulfate, ferrous sulfate, manganese sulfate, and copper sulfate, and their mass accounts for 2% - 6% of the total system. The gelation aids in the S2 step include polyvinyl alcohol and polylactic acid, and their total mass accounts for 5% - 10% of the total system.

[0010] Preferably, the gelation in the S2 step is carried out by cross-linking reaction in a low-temperature environment of 4 - 10°C, the reaction time is 30 - 60 minutes, and the obtained particle size is 100 - 500 nanometers.

[0011] Preferably, in the S3 step, the mass of chitosan accounts for 0.5% - 2% of the total system, the mass of phospholipid accounts for 0.1% - 1% of the total system, and the reaction is carried out at 50 - 60°C for 30 - 60 minutes to form a stable interfacial bilayer structure.

[0012] Preferably, the outer shell controlled-release layer in the S4 step is formed by cross-linking sodium alginate and calcium chloride, and simultaneously contains sodium polyacrylate with a mass accounting for 0.5% - 1% of the total system. The reaction temperature is controlled below 25°C, and the reaction time is 30 - 45 minutes.

[0013] Preferably, the pH adjustment range in the S5 step is 6.0 - 6.5, the particle size is controlled by membrane filtration or centrifugation method, and the obtained product is water-soluble suspended particles with a particle size of 100 - 500 nanometers.

[0014] The present invention also provides a fertilization method for the water-soluble fertilizer prepared by the method for preparing a water-soluble fertilizer rich in various active amino acids, including: Rhizosphere response fertilization: During the seedling stage to the root development stage of the crop, use a water-soluble fertilizer with a concentration of 0.5% - 1%, apply 5 - 8 L per mu, apply once every 3 - 5 days, and activate root growth through drip irrigation or local fertilization, initiate the middle layer response of the fertilizer, the middle membrane layer responds rapidly in a slightly acidic environment, activate rhizosphere stimulation, and promote early rooting; Precision fertilization by time period: During the rapid growth period of crops, select the night fertilization time period, use water-soluble fertilizer with a concentration of 2.5% - 3%, apply 15 - 20 L per mu, and apply once every 7 - 10 days. Utilize the ion responsiveness of the fertilizer outer shell layer to accelerate release. The outer controlled-release layer responds to the change of ion osmotic pressure in the rhizosphere to achieve synchronous release at night and accelerate nutrient supply. Dynamic fertilization adjustment: From the flowering period to the fruit swelling period, dynamically adjust the fertilizer concentration according to the change of rhizosphere pH. Use water-soluble fertilizer with a concentration of 1.5% - 2%, apply 10 - 12 L per mu, and apply once every 5 - 7 days. Control the release rate through drip irrigation. Fertilization during the slow-release period: During the mature period of crops, use water-soluble fertilizer with a low concentration of 0.5% - 1%, apply 5 - 8 L per mu, and apply once every 10 - 14 days to maintain the balance between micro-stimulation in the rhizosphere and nutrient supply and avoid nutrient excess.

[0015] The present invention provides a preparation method of water-soluble fertilizer rich in various active amino acids. It has the following beneficial effects: 1. By adopting low-temperature crosslinking and two-component synergistic gelation structure design, the present invention achieves the technical effects of highly stable core particle size, dense structure and not easy to disperse. Compared with the prior art that often uses a single polymer gel, such as polyvinyl alcohol or gelatin, for structure construction and it is difficult to maintain a stable particle size distribution during storage, the technical defect of formulation delamination and function failure caused by particle size drift is solved.

[0016] 2. By constructing a composite structure of an intermediate responsive membrane layer and an external controlled-release coating, the present invention realizes a release control mechanism of rapid response in a weak acid environment and subsequent slow-release propulsion. Compared with the prior art that relies on single-layer membrane coating or static pore controlled release, whose structural responsiveness is poor and the release is discontinuous, this solution effectively breaks through the structural response obstacle of "too fast release or release lag".

[0017] 3. By adopting the "structure-function integration" particle collaborative design concept, the present invention realizes good suspension and repeatable dispersibility of the product. Among current similar products, problems such as uneven coating or loose core layer are common, resulting in stratification and flocculation phenomena in the suspension after long-term storage. Starting from the microscopic structure of the particles, this technical solution solves the practical application pain points of poor product dispersibility and difficult to shake evenly. Brief description of the drawings

[0018] Figure 1 It is a flowchart of the preparation method of the present invention. Detailed implementation manners

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

[0020] Please refer to the attached Figure 1 , and the present invention provides a preparation method of a water-soluble fertilizer rich in various active amino acids through the following embodiments.

[0021] Example 1: General amino acid-microelement controlled-release water-soluble fertilizer Preparation of amino acid solution (S1): Types of amino acids: 4 g of glutamic acid, 4 g of lysine, 3 g of proline, 3 g of serine, 3 g of leucine; Total dosage: 17 g (accounting for 28.3% of the total system); Dissolution solution: 200 mL of pH 6.2 phosphate buffer, stirred for 10 min to form a precursor amino acid solution.

[0022] Construction of the nutrient core layer (S2): Microelement salts: 1.5 g of zinc sulfate, 1 g of manganese sulfate (accounting for 4.2% of the total system); Gelling agent: 5 g of polyvinyl alcohol, 3 g of polylactic acid (accounting for 7.5% of the total system); Condition: Stir and crosslink at 8 °C for 45 minutes, and dropwise add 0.2% glutaraldehyde; Particle size control: about 350 nm, showing semi-transparent gel particles.

[0023] Coating of the intermediate response layer (S3): Chitosan: 1.2 g (1.8%); Phospholipid: 0.6 g (0.9%); Temperature control: React at 55 °C for 40 minutes to obtain a stable bimolecular membrane structure.

[0024] Construction of the outer controlled-release layer (S4): Sodium alginate: 2% w / v, calcium chloride: 1.5%; Sodium polyacrylate: 0.6 g (0.9%); Condition: Reaction temperature is 22 °C, time is 40 minutes, to form the outer shell.

[0025] pH and dosage form control (S5): Adjust the pH to 6.3 and centrifuge; Obtain a light yellow suspension with a particle size of 320–370 nm.

[0026] Example 2: High Amino Acid Concentration Water Soluble Fertilizer Preparation of Amino Acid Solution (S1): Types of amino acids: 6 g of glutamic acid, 5 g of lysine, 5 g of proline, 4 g of valine, 4 g of leucine, 4 g of serine; Total dosage: 28 g (accounting for 31.1% of the total system); Solvent: 200 mL of pH 6.4 weakly acidic Tris buffer solution, stirred and ultrasonically treated for 5 min.

[0027] Construction of Nutritional Core Layer (S2): Trace element salts: 2 g of ferrous sulfate, 1.2 g of copper sulfate (accounting for 5.1% of the total system); Gelling agent: 4.5 g of polyvinyl alcohol, 4.5 g of polylactic acid (accounting for 9% of the system); Conditions: low temperature (5 °C), crosslinking time 50 minutes; Particle size analysis: 280–320 nm, evenly distributed.

[0028] Coating of Intermediate Response Layer (S3): Chitosan: 1.5 g (1.7%); Phospholipid: 0.7 g (0.8%); Coating conditions: react at 58 °C for 45 minutes to form a stable flexible bilayer membrane.

[0029] Construction of Outer Shell Controlled Release Layer (S4): The sodium alginate gel layer is formed by the dropping method (concentration: 1.8%); The addition amount of sodium polyacrylate is 1.0% (2 g); Control the reaction temperature at 20 °C and the time at 30 minutes to form a dense outer shell.

[0030] pH and Dosage Form Control (S5): Adjust the pH to 6.0–6.2, and use membrane filtration (0.45 µm); A highly active water-soluble suspension with good stability is obtained, showing a milky white and slightly viscous state, pH 6.1.

[0031] Example 3: Low Temperature Stable Granular Water Soluble Fertilizer Preparation of Amino Acid Solution (S1): Types of amino acids: 3 g of glutamic acid, 3 g of lysine, 3 g of valine, 2 g of proline, 2 g of serine; Total dosage: 13 g (accounting for 21.6% of the total system); Solution system: 250 mL of weakly acidic acetic acid buffer solution (pH 6.0), stirred at room temperature.

[0032] Construction of Nutritional Core Layer (S2): Trace element salts: Manganese sulfate 1.2 g, zinc sulfate 0.8 g (total accounting for 3.3% of the system); Gel assistant: Polyvinyl alcohol 4 g, polylactic acid 2.5 g (total proportion 6.5%); Preparation conditions: React at 4 °C for 60 minutes, and add 0.1% glutaraldehyde for stable cross-linking.

[0033] Coating of the intermediate response layer (S3): Chitosan: 0.9 g (1.2%); Phospholipid: 0.4 g (0.5%); Temperature control: React at 50 °C for 35 minutes to form a lightweight bilayer membrane.

[0034] Construction of the outer shell controlled-release layer (S4): Adopt the cross-linking method of 1.5% sodium alginate + 1.5% CaCl2, combined with 0.5% sodium polyacrylate; Condition control: 22 °C, react for 45 minutes; The obtained product is low-temperature redispersible gel particles with a particle size of about 300 nm.

[0035] pH and dosage form control (S5): Adjust the final pH to 6.5, and make a powder-type water-soluble fertilizer after spray drying; The finished product is a light yellow free-flowing powder, with the particle size controlled within 480 nm, suitable for dry powder dropping and dissolving application or spraying and recombination.

[0036] Comparative example 1-1: Do not add polylactic acid In step S2, only add 5 g of polyvinyl alcohol and do not add polylactic acid.

[0037] Mechanism explanation: If the gelation assistant in step S2 does not contain polylactic acid or its dosage is less than 5% of the total system, the core particle structure is unstable, resulting in poor adhesion of the controlled-release layer and out-of-control particle size distribution, ultimately affecting the dispersion and release characteristics of the fertilizer in water.

[0038] Comparative example 1-2: Cancel the low-temperature cross-linking condition Set the cross-linking temperature in step S2 to room temperature (25 °C), and keep the other conditions unchanged.

[0039] Mechanism explanation: If the gelation reaction temperature in step S2 is higher than 10 °C, the cross-linking rate is out of control, affecting the uniformity of the colloidal network, causing particle size enlargement and system instability, and affecting the controlled-release behavior.

[0040] Comparative example 2-1: Remove phospholipid In step S3, do not add phospholipid and only retain chitosan.

[0041] Mechanism description: If the phospholipid mass ratio in step S3 is lower than 0.1% or absent, a stable bimolecular membrane structure cannot be formed, thereby reducing the controlled release ability of the response layer in the rhizosphere low pH environment.

[0042] Comparative example 2-2: Coating temperature reduced to 30 °C In step S3, the reaction temperature is reduced from 55–60 °C to 30 °C.

[0043] Mechanism description: If the coating temperature in step S3 is lower than 50 °C, the interfacial polymerization during the formation of the bimolecular membrane is hindered, and a stable charge / hydrophobic interface cannot be established, resulting in a decrease in structural responsiveness.

[0044] Comparative example 3-1: Sodium polyacrylate is not added In step S4, sodium polyacrylate is removed from the outer shell layer, and only sodium alginate and CaCl2 are cross-linked.

[0045] Mechanism description: If the sodium polyacrylate content in the outer shell controlled release layer is lower than 0.3%, the osmotic responsiveness of the system to the ionic environment is reduced, and the release rate cannot be regulated as needed, resulting in "slow but uncontrolled".

[0046] Comparative example 3-2: pH is not controlled, and the final pH is 7.1 In step S5, the final system pH is not adjusted, and the reaction system naturally reaches pH 7.1 by default.

[0047] Mechanism description: If the final product pH is higher than 6.8, the amino acids in the system are easily oxidized and degraded under weak base conditions, resulting in a decrease in activity, a darker product color, and a loss of bioavailability.

[0048] Experiment 1: Particle size stability and suspension performance test I. Experimental purpose Verify whether the controlled release amino acid water-soluble fertilizer prepared in Example 1 has good particle size stability and long-term suspension performance on the premise of complete structural components and preparation conditions, and compare it with Comparative example 1 (without adding polylactic acid) and Comparative example 2 (cross-linking at room temperature).

[0049] II. Experimental materials and equipment Sample source: Water-soluble fertilizer suspensions obtained from Example 1, Comparative example 1, and Comparative example 2.

[0050] Instrumentation: Nanoparticle size analyzer (Malvern Zetasizer Nano ZS90); Visible light spectrophotometer (for transmittance evaluation); Constant temperature storage box (25 °C, protected from light); Transparent glass centrifuge tube (100 mL); Conventional equipment such as electronic balances, magnetic stirrers, pH meters, etc.

[0051] III. Experimental Procedures 1. Particle Size Stability Test (1) Take three groups of samples respectively, and use a particle size analyzer to measure the initial average particle size (D50), and record the data; (2) Seal and store the samples in an incubator (25°C, protected from light) for 72 hours; (3) Measure the average particle size again after 72 hours, and calculate the change rate (ΔD%): , where is the particle size change rate (percentage), indicating the relative amplitude of particle size growth during storage, and is used to measure the structural stability of the particle system; is the initial average particle size, that is, the average particle diameter measured immediately after sample preparation, with the unit of nanometer (nm); is the average particle size after 72 hours of storage, with the same unit of nanometer (nm).

[0052] 2. Suspension Performance Test (1) Take three groups of samples and put them into 100 mL glass tubes, and let them stand for 30 days; (2) Observe every day whether there are obvious sedimentation layers, stratification interfaces, flocs, etc.; (3) Take a sample on the 30th day, shake it evenly for 10 seconds, observe the time required for redispersion, and measure the supernatant transmittance (λ = 600 nm) as the redispersibility index; (4) Score according to the following criteria (0–5 points) to evaluate the suspension integrity: IV. Experimental Data Recording Table 1 Comparison of Particle Size and Suspension Performance of Three Groups of Water-Soluble Fertilizer Samples V. Experimental Conclusions Judging from the experimental results, the water-soluble fertilizer particles prepared in Example 1 showed excellent performance in terms of particle size stability and suspension performance. This performance is directly attributed to the synergistic gelation effect of polyvinyl alcohol and polylactic acid in the core structure. As a hydrophobic chain segment, polylactic acid can form multi-point hydrogen bonds and spatial physical entanglement structures with polyvinyl alcohol under low-temperature cross-linking conditions, enabling the core colloidal particles to form a dense and tough three-dimensional network. This structure not only improves the core strength but also provides an ideal carrier basis for subsequent film coating. In Comparative Example 1, polylactic acid was not added, resulting in a loose and uneven internal network of the particles, and the structure was prone to swelling and breaking in water, and finally obvious sedimentation and stratification occurred during storage.

[0053] The stable formation of the intermediate response layer also depends on the integrity of the core structure and the particle size uniformity. In Example 1, the particle size distribution of the colloidal particles was controlled by slow cross-linking under low-temperature conditions, making it more conducive to the uniform interfacial coating of chitosan and phospholipids. This structure can maintain good suspension of the particles during storage and dispersion, and is beneficial to the interfacial response during subsequent rhizosphere release. In Comparative Example 2, due to the lack of low-temperature cross-linking, the particle size control during the gel formation process was inaccurate, resulting in uneven coating of the subsequent intermediate film and unstable interfacial tension distribution, thus causing flocculation and stratification during storage.

[0054] In summary, the improvement of particle size stability and suspension performance is not the result of a single parameter, but stems from the synergistic structure design from the core to the shell. The stable core constructed by polylactic acid and polyvinyl alcohol at low temperature provides a physical stability basis for the intermediate response layer and the outer controlled-release layer, and also ensures that the whole system can remain dispersed in water for a long time without precipitation, reflecting the actual conversion ability of the "structure-function integration" controlled-release concept of the present invention. Experiment 2: pH-responsive release behavior test I. Experimental purpose Verify whether the controlled-release water-soluble fertilizer prepared in Example 1 has stable and adjustable nutrient release behavior in a weakly acidic environment (simulating the rhizosphere environment), and compare it with Comparative Example 1 (lacking a structurally stable core) and Comparative Example 2 (insufficient conditions for forming the coating film).

[0055] II. Experimental principle In this experiment, a phosphate buffer solution (pH 5.5) was used to simulate the weak acid environment caused by the secretion of organic acids by plant roots. The release behavior of amino acids in each sample was observed. Samples were taken at time nodes to measure the release amount, and release curves were plotted to evaluate the controlled-release performance and response rules under different structures.

[0056] III. Experimental materials and equipment Samples: Example 1, Comparative Example 1, Comparative Example 2 (diluted to 1% w / v with the same concentration).

[0057] Buffer system: pH 5.5 phosphate buffer solution.

[0058] Detection reagent: Ninhydrin colorimetric reagent for quantitative detection of free amino acids.

[0059] Instruments: Spectrophotometer (570 nm), thermostatic oscillator (37 °C), sampling syringe, microcentrifuge tubes, etc.

[0060] IV. Experimental steps System establishment: Weigh 1 g of each group of samples, add them to 50 mL of pH 5.5 buffer solution preheated to 37 °C, and place them in a thermostatic oscillator (rotation speed 100 rpm) and shake continuously; Sampling and determination: Take 2 mL of the supernatant at the set time points (6 h, 12 h, 24 h, 48 h), filter it, and use the ninhydrin colorimetric method to colorimetrically determine the content of the released amino acids (calculated as glutamic acid equivalent); Data processing: Record the cumulative release amount (mg) at each time point and convert it into the release rate (%), and draw the release curve; compare the initial release rate, overall release efficiency, and rhythm control ability.

[0061] V. Experimental data record Table 2 Cumulative amino acid release rate (%) of each sample at pH 5.5 VI. Experimental conclusion The results of Experiment 1 clearly verified the synergistic action mechanism of each functional component in the three-layer controlled-release structure of the present invention from the perspectives of structural stability and formulation performance. The combined gelation of polyvinyl alcohol and polylactic acid can form a tightly cross-linked physical network structure under low-temperature conditions, enabling the nutrient core layer to have strong particle size stability and colloidal mechanical strength. This structure not only effectively resists particle aggregation and sedimentation caused by shear force or gravity in the aqueous phase environment but also provides a stable geometric basis for the subsequent smooth coating of the intermediate layer and the outer shell layer. The rapid sedimentation and particle size growth of Comparative Example 1 are exactly the manifestations of the loose and easily disintegrated gel structure due to the lack of polylactic acid.

[0062] In addition, the low-temperature cross-linking process has a key regulatory function in the formation of the formulation structure of the present invention. Compared with the reaction at room temperature, the lower temperature can slow down the movement rate of molecular chain segments in the colloid, promoting uniform cross-linking and the controllable formation of microstructures. In Comparative Example 2, the reaction was carried out under uncontrolled temperature conditions. Although a preliminary structure was formed, its particle size distribution was more extensive, and the film coating thickness was uneven due to the non-uniformity of the inner core surface during the film coating stage, and finally, problems such as interface structure instability and flocculation precipitation occurred during storage. It can be seen that the temperature control process not only affects the inner core structure but also indirectly determines whether the outer layer structure can be successfully constructed and remain stable for a long time.

[0063] More importantly, the present invention organically integrates the controlled-release behavior with the particle structure stability through the design concept of "structure–function integration". The high-scoring suspension, small particle size change rate, and excellent dispersibility shown by Example 1 in the experiment are exactly the manifestations of the synergistic action of this multi-level structure. The functions of different layers are clear, the responses are independent but coupled and coordinated, which not only ensures the storage stability before application but also provides a solid structural platform for the subsequent responsive release.

[0064] Experiment 3: Test of controlled-release persistence and slow-release effect I. Experimental purpose Evaluate the slow-release persistence of the controlled-release water-soluble fertilizer prepared in Example 1 of the present invention in a neutral environment (simulated irrigation water or neutral soil water), and compare it with Comparative Example 1 and Comparative Example 2.

[0065] II. Experimental Principle By continuously soaking under neutral conditions and sampling at regular intervals, measure the cumulative release amount of amino acids at different time points, and analyze the controlled-release ability, duration, and release curve shape of the sample. Compared with burst-release fertilizers, a high-quality controlled-release system should have a stable release in the early stage and a slow increase in the middle and late stages, reflecting the characteristics of "slow release - long-term effect".

[0066] III. Experimental Materials and Equipment Samples: Example 1, Comparative Example 1, Comparative Example 2 (at the same concentration of 1% w / v).

[0067] Buffer medium: pH 7.0 phosphate buffer solution.

[0068] Chromogenic reagent: Detect free amino acids by the ninhydrin method.

[0069] Instrumentation: Spectrophotometer (570 nm), constant temperature oscillator (37 °C), sampler, filter membrane, and other conventional experimental apparatus.

[0070] IV. Experimental Procedures Sample preparation and soaking: Weigh 1 g of each sample, add 50 mL of pH 7.0 buffer solution, and place it in a constant temperature oscillator at 37 °C (90 rpm) for continuous soaking.

[0071] Sampling and detection at regular intervals: Sampling once every 24 hours until the 10th day; each time, take 2 mL of the supernatant and measure the content of free amino acids therein and record the cumulative release amount.

[0072] Data sorting and analysis: Calculate the cumulative release amount and its proportion (release rate %) of each group of samples, and compare the release rate, control rhythm, and final total release amount.

[0073] V. Experimental Data Record Table 3 Amino acid controlled-release performance data (cumulative release rate %) of each sample under neutral conditions VI. Experimental Conclusions The results of Experiment 1 fully demonstrate the advantages of the constructed three-layer controlled-release structure in terms of particle size stability and suspension performance. Its performance directly stems from the triple synergistic mechanism of "core-responsive-controlled release" in the structure construction. In Example 1, polyvinyl alcohol and polylactic acid were crosslinked together under low-temperature conditions to form a dense and uniform core matrix. The addition of polylactic acid not only introduced hydrophobic segments to enhance the internal toughness of the colloid but also improved the morphological stability of the entire particle structure through spatial entanglement and multi-point hydrogen bonding. This core structure enables the size of the colloidal particles to remain stable during storage in water, avoiding drastic changes in particle size caused by particle water absorption and swelling or flocculation, providing a basic support for the long-term suspension of the entire system.

[0074] The effective coating of the intermediate responsive layer is also closely related to the particle size control of the core structure. In the present invention, the narrow particle size distribution brought about by low-temperature crosslinking enables a more uniform interfacial assembly of chitosan and phospholipids, contributing to the formation of a complete and continuous intermediate membrane layer, further enhancing the interfacial stability between particles. This layer serves both as a functional structure for pH-responsive release and as a spatial barrier to inhibit particle aggregation. In Comparative Example 2, due to the rough and uneven surface of the core structure, the film layer is difficult to grow continuously, resulting in unstable energy distribution at the interface, and the particles are more likely to adhere or aggregate irregularly during storage, ultimately showing obvious sedimentation and stratification.

[0075] Furthermore, from the perspective of the overall structural-functional synergy, the performance characteristics such as low particle size change rate, good redispersibility, and high light transmittance exhibited by Example 1 are the comprehensive manifestation of the multi-level structural linkage regulation. The stable core structure provides physical support, the responsive membrane layer inhibits the aggregation behavior, and the outer coating forms a hydrophobic protective shell to further resist environmental disturbances. This hierarchical and functionally cooperative structural system is the concentrated embodiment of the "interface regulation-structure stability-functional release" mechanism of the present invention, enabling the preparation to maintain good dispersibility and controllability during storage and application.

[0076] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of a water-soluble fertilizer rich in various active amino acids, characterized in that, It includes the following steps: S1. Prepare the amino acid solution: Dissolve various free amino acids or polypeptides in a buffer solution to form a precursor amino acid solution; S2. Construct the nutrient core layer: Add one or more types of soluble trace element salts and a gelation aid to the precursor amino acid solution to form gel-like particles; S3. Form the intermediate response layer: Coating the core particles with chitosan and phospholipids to form a bilayer membrane structure; S4. Construct the outer controlled-release layer: Further coating the bilayer membrane structure particles with sodium alginate and sodium polyacrylate to form an outer shell; S5. Adjust the pH and control the final dosage form: Adjust the pH of the coated particles, control the particle size, and prepare a water-soluble liquid or powder-type water-soluble fertilizer product containing uniformly dispersed coated particles.

2. The preparation method of a water-soluble fertilizer rich in various active amino acids according to claim 1, characterized in that, In the S1 step, the amino acids include at least five of glutamic acid, lysine, proline, valine, serine, and leucine, and the total mass of the amino acids accounts for 15% - 30% of the final system.

3. The preparation method of a water-soluble fertilizer rich in various active amino acids according to claim 1, characterized in that, The trace element salts in the S2 step are selected from one or more of zinc sulfate, ferrous sulfate, manganese sulfate, and copper sulfate, and their mass accounts for 2% - 6% of the total system. The gelation aid in the S2 step includes polyvinyl alcohol and polylactic acid, and their total mass accounts for 5% - 10% of the total system.

4. A preparation method of a water-soluble fertilizer rich in various active amino acids according to claim 1, characterized in that, The gelation in the S2 step is carried out by cross-linking reaction under a low-temperature environment of 4 - 10°C, the reaction time is 30 - 60 minutes, and the particle size of the obtained particles is 100 - 500 nanometers.

5. The preparation method of a water-soluble fertilizer rich in various active amino acids according to claim 1, characterized in that, In the S3 step, the mass of chitosan accounts for 0.5% - 2% of the total system, the mass of phospholipids accounts for 0.1% - 1% of the total system, and the reaction is carried out at 50 - 60°C for 30 - 60 minutes to form a stable interfacial bilayer structure.

6. The preparation method of a water-soluble fertilizer rich in various active amino acids according to claim 1, characterized in that, The outer controlled-release layer in the S4 step is formed by cross-linking sodium alginate with calcium chloride, and also contains sodium polyacrylate with a mass accounting for 0.5% - 1% of the total system. The reaction temperature is controlled below 25°C, and the reaction time is 30 - 45 minutes.

7. The preparation method of a water-soluble fertilizer rich in various active amino acids according to claim 1, characterized in that, The pH adjustment range in the S5 step is 6.0 - 6.5, the particle size is controlled by membrane filtration or centrifugation method, and the obtained product is water-soluble suspended particles with a particle size of 100 - 500 nanometers.

8. A fertilization method for a water-soluble fertilizer prepared by the method for preparing a water-soluble fertilizer rich in various active amino acids according to any one of claims 1-7, characterized in that, It includes: Rhizosphere response fertilization: During the seedling stage to the root development stage of the crop, use a water-soluble fertilizer with a concentration of 0.5% - 1%, apply 5 - 8L per mu, apply once every 3 - 5 days, and activate root growth and initiate the intermediate layer response of the fertilizer through drip irrigation or local fertilization; Period precision control fertilization: During the rapid growth period of the crop, select the night fertilization period, use a water-soluble fertilizer with a concentration of 2.5% - 3%, apply 15 - 20L per mu, apply once every 7 - 10 days, and utilize the ion responsiveness of the fertilizer outer shell layer to accelerate release; Dynamic fertilization adjustment: During the flowering period to the fruit swelling period, dynamically adjust the fertilizer concentration according to the change of rhizosphere pH, use a water-soluble fertilizer with a concentration of 1.5% - 2%, apply 10 - 12L per mu, apply once every 5 - 7 days, and control the release rate through drip irrigation; Slow-release period fertilization: During the mature period of the crop, use a water-soluble fertilizer with a low concentration of 0.5% - 1%, apply 5 - 8L per mu, and apply once every 10 - 14 days.

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