Functional water-soluble fertilizer containing chitooligosaccharide lactate and preparation method thereof

Abstract

The present application belongs to the field of functional water-soluble fertilizer, and provides a functional water-soluble fertilizer containing chitosan oligosaccharide lactate and a preparation method thereof.The present application forms an ion complex through electrostatic interaction of chitosan oligosaccharide lactate and gamma-polyglutamic acid potassium salt, and performs water-phase compounding and spray drying of urea, potassium dihydrogen phosphate, potassium nitrate, trace elements and acid-base buffer components, to form a weak-acid high-water-soluble complex fertilizer system, realize complex dispersion in a high-salt system, filtration stability, chitosan oligosaccharide lactate retention and water-solubility consideration, reduce the risk of precipitation and inactivation caused by multivalent metal ions, solve the problem that functional components are difficult to be effectively retained and dispersed and stable, and trace elements are difficult to be effectively and stably stored, and the present application is suitable for drip irrigation, flushing, foliar spraying and facility cultivation.

Description

Technical Field

[0001] This invention relates to the field of functional water-soluble fertilizers, specifically to a functional water-soluble fertilizer containing chitosan oligosaccharide lactate and its preparation method. Background Technology

[0002] Water-soluble fertilizers are suitable for high-frequency fertigation applications such as drip irrigation, fertigation, foliar spraying, and greenhouse cultivation. They require solid products to disperse rapidly in water, have low water-insoluble matter, low precipitation risk, and good compatibility with micronutrients. Macronutrient water-soluble fertilizers typically use nitrogen, phosphorus, and potassium as the main nutrients, combined with micronutrients such as magnesium, zinc, iron, boron, manganese, and molybdenum to meet the absorption needs of different crops during their vegetative growth, reproductive growth, and under adverse conditions. γ-Polyglutamic acid, as a biodegradable anionic polymer, has been shown in studies to have potential for fertilizer synergism, promoting nutrient absorption, and improving water retention in agriculture. Chitosan and its oligosaccharides have also received widespread attention for their applications in inducing plant resistance and biostimulation. Therefore, combining functional oligosaccharide components with conventional water-soluble fertilizer systems is of great significance for improving fertilizer water solubility, utilization of effective components, and compound stability.

[0003] Existing functional water-soluble fertilizers typically improve fertilizer application by adding chitosan, polyglutamic acid, humic acid, amino acids, or other biostimulants. However, in systems with high salt content, high ionic strength, and the coexistence of multivalent metal ions, functional polyelectrolytes are prone to association, flocculation, filtration loss, or precipitation after storage. Chinese patent CN110483208A discloses an organic water-soluble chitosan functional fertilizer, involving a compound of chitosan, polyglutamic acid, and various nutrients. However, its focus is on the combination of organic fertilizer and multifunctional components, without systematically controlling the filtration retention, ion complexation state, batch addition sequence of micronutrients, and weakly acidic pH window of chitosan oligosaccharide lactate in high-salt water-soluble fertilizers. While agricultural industry standards exist for testing water-insoluble matter and pH in water-soluble fertilizers, and corresponding detection methods exist for micronutrients and NPK content, further research is needed to address how to simultaneously ensure effective retention, dispersion stability, and storage stability of functional components at the formulation level. Summary of the Invention

[0004] The purpose of this invention is to provide a functional water-soluble fertilizer containing chitosan oligosaccharide lactate and its preparation method, thereby solving the problem that functional oligosaccharide components are difficult to stably disperse, effectively retain, and store for a long time in high-salt water-soluble fertilizers.

[0005] In this invention, functional water-soluble fertilizer refers to a water-soluble fertilizer containing a complex system of chitosan oligosaccharide lactate and γ-polyglutamic acid potassium salt, and the quality control objects are water solubility, chitosan oligosaccharide lactate retention rate after filtration, water solubility after storage, and stability of micronutrient compounding.

[0006] This invention utilizes the ionic complexation of chitosan oligosaccharide lactate and γ-polyglutamic acid potassium salt, weakly acidic pH control, and the batch addition of trace elements to mutually correct the retention advantage brought about by enhanced ionic binding and the dispersion stability required to inhibit flocculation, thereby achieving a balance between the activity of multivalent nutrients and their storage water solubility. The chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ionic complex referred to in this invention refers to the aqueous dispersion system or its dried solid obtained by the aforementioned filtration step, formed by the electrostatic interaction of chitosan oligosaccharide lactate and γ-polyglutamic acid potassium salt under the specified mass ratio, pH, temperature, and aqueous phase mixing conditions. The dispersion and filtration stability of this ionic complex are characterized by at least one of the following quality control indicators: water-insoluble matter, chitosan oligosaccharide lactate retention rate after 0.45 μm filtration, particle size, and zeta potential.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A functional water-soluble fertilizer containing chitosan oligosaccharide lactate, based on 100 wt% of the total mass of the finished functional water-soluble fertilizer, comprises the following components converted from the corresponding feed ingredients: The chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ionic complex is 0.20-5.00 wt%, wherein the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ionic complex is formed by the electrostatic interaction between chitosan oligosaccharide lactate and γ-polyglutamic acid potassium salt, wherein the γ-polyglutamic acid potassium salt is formed by the neutralization of γ-polyglutamic acid with potassium hydroxide; Urea 5.00-40.00 wt%; Potassium dihydrogen phosphate 10.00-60.00 wt%; Potassium nitrate 5.00-50.00 wt%; Magnesium sulfate heptahydrate 0.20-8.00 wt%; Zinc sulfate heptahydrate 0.05-3.00 wt%; Ferrous sulfate heptahydrate 0.05-3.00 wt%; Boric acid 0.02-3.00 wt%; Manganese sulfate monohydrate 0.01-1.00 wt%; Ammonium molybdate tetrahydrate 0.001-0.20 wt%; Optional calcium nitrate tetrahydrate 0.10-3.00 wt%, when containing the calcium nitrate tetrahydrate, the mass ratio of the calcium nitrate tetrahydrate to the potassium dihydrogen phosphate is 0.02-0.30:1; Citric acid monohydrate 0.01-1.50 wt%; Moisture 0.50-5.00wt%; The mass ratio of chitosan oligosaccharide lactate to γ-polyglutamic acid potassium salt in the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex is 1:0.50-4.00; the pH value of the functional water-soluble fertilizer when formulated into a 10wt% aqueous solution is 5.50-6.80, the water-insoluble matter is 0.05-0.80wt%, and the chitosan oligosaccharide lactate retention rate after 0.45μm filtration is 80.00-99.00%; the content of the above components is selected within the range that makes the sum of the contents of all components in the functional water-soluble fertilizer 100wt%, wherein the content of potassium nitrate is adjusted according to the content of other components within the range.

[0008] In this invention, the component content calculated based on the corresponding feed ingredients refers to the calculation based on the mass of each of the listed feed ingredients added to the functional water-soluble fertilizer finished product system; the potassium hydroxide used for neutralizing γ-polyglutamic acid is included in the γ-polyglutamic acid potassium salt formation process, the potassium ions introduced by the potassium hydroxide aqueous solution used for pH fine adjustment are included in the potassium element detection caliber of the finished product, and the total mass of the finished product is 100wt% by adjusting the amount of potassium nitrate.

[0009] Furthermore, the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex is prepared by the following steps: A1. Provides an aqueous solution of chitosan oligosaccharide lactate and an aqueous solution of potassium γ-polyglutamate, wherein the aqueous solution of chitosan oligosaccharide lactate contains 1.00-15.00 wt% chitosan oligosaccharide lactate, and the aqueous solution of potassium γ-polyglutamate contains 1.00-30.00 wt% potassium γ-polyglutamate. A2. The aqueous solution of chitosan oligosaccharide lactate and the aqueous solution of γ-polyglutamic acid potassium salt are mixed at a mass ratio of chitosan oligosaccharide lactate to γ-polyglutamic acid potassium salt of 1:0.50-4.00, and stirred at 25-45℃ for 30-120 min at pH 5.20-6.80 to obtain the composite mixture. A3. Filter the composite mixture to obtain the aqueous dispersion of the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex.

[0010] Further, in step A2, the composite is carried out under an absolute pressure of 0.09-0.11 MPa and an air atmosphere; the composite is terminated when the pH change of the composite mixture does not exceed 0.20 within 30 minutes and no flocculent matter is retained after filtration through a 100 μm sieve; the filtration in step A3 uses a 100-200 mesh sieve; the aqueous dispersion of the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex obtained in step A3 is dried at 45-75℃ for 2-8 hours to obtain a solid chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex; the quality control parameters of the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex are: water-insoluble matter of 0.05-0.80 wt%, and chitosan oligosaccharide lactate retention rate of 80.00-99.00% after 0.45 μm filtration.

[0011] Furthermore, the γ-polyglutamic acid potassium salt aqueous solution in step A1 is prepared by the following steps: B1. Add 100 parts by weight of γ-polyglutamic acid to 300-3000 parts by weight of deionized water and stir at 20-40℃ for 0.5-2.0h to obtain γ-polyglutamic acid hydrated solution; B2. Add a 5.00-30.00 wt% potassium hydroxide aqueous solution to the γ-polyglutamic acid hydrate solution, controlling the temperature at 20-40℃ and the pH at 6.50-8.00 during the addition process, and continue stirring for 0.5-2.0 h to obtain a γ-polyglutamic acid potassium salt aqueous solution. B3. The neutralization adjustment is terminated when the pH change of the γ-polyglutamic acid potassium salt aqueous solution does not exceed 0.20 within 30 minutes; B4. The γ-polyglutamic acid potassium salt aqueous solution is filtered through a 100-200 mesh filter and then adjusted by adding water or concentration to obtain a γ-polyglutamic acid potassium salt aqueous solution with a solid content of 1.00-30.00 wt% and a carboxyl potassium salt concentration of 70.00-100.00 mol%.

[0012] Furthermore, the chitosan oligosaccharide lactate aqueous solution in step A1 is prepared by the following steps: C1. Add 100 parts by weight of chitosan oligosaccharide lactate to 600-10000 parts by weight of deionized water, wherein the number average molecular weight of chitosan oligosaccharide lactate is 300-5000 Da; C2. Stir at 20-40℃ and 0.09-0.11MPa absolute pressure for 20-60 min to obtain a crude solution of chitosan oligosaccharide lactate; C3. The pH of the crude chitosan oligosaccharide lactate solution was adjusted to 4.80-6.50 using citric acid monohydrate and a potassium hydroxide aqueous solution with a mass concentration of 5.00-30.00 wt%. C4. The crude chitosan oligosaccharide lactate solution after pH adjustment is filtered through a 100-200 mesh filter, and after water replenishment or concentration adjustment, an aqueous solution of chitosan oligosaccharide lactate is obtained, wherein the water-insoluble matter in the aqueous solution of chitosan oligosaccharide lactate is not higher than 1.00 wt%.

[0013] Furthermore, the magnesium sulfate heptahydrate, zinc sulfate heptahydrate, ferrous sulfate heptahydrate, boric acid, manganese sulfate monohydrate, and ammonium molybdate tetrahydrate are added through the following steps: D1. Prepare aqueous solutions of magnesium sulfate heptahydrate, zinc sulfate heptahydrate, ferrous sulfate heptahydrate, boric acid, manganese sulfate monohydrate and ammonium molybdate tetrahydrate with a mass concentration of 1.00-30.00 wt% respectively. D2. Mix the aqueous dispersion of chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex obtained in step A3 with urea, potassium dihydrogen phosphate and potassium nitrate, and then add the aqueous solutions obtained in step D1 in batches at 25-45℃. The addition time for each batch is 5-30 min, and the total addition time is 30-120 min. D3. During the addition process, control the pH to 5.50-6.80; D4. After the addition is complete, continue stirring for 20-60 minutes until the resulting mixture has no visible precipitate and the water-insoluble matter is no more than 0.80 wt%.

[0014] Furthermore, the functional water-soluble fertilizer also includes calcium nitrate tetrahydrate. Based on the total mass of the finished functional water-soluble fertilizer product being 100 wt%, the content of calcium nitrate tetrahydrate is 0.10-3.00 wt%, and the mass ratio of calcium nitrate tetrahydrate to potassium dihydrogen phosphate is 0.02-0.30:1. The sum of the content of calcium nitrate tetrahydrate and the content of the remaining components in the functional water-soluble fertilizer is 100 wt%.

[0015] Furthermore, after the functional water-soluble fertilizer is formulated into an aqueous solution with a mass fraction of 10 wt%, the water-insoluble matter content is 0.05-0.80 wt%, and the chitosan oligosaccharide lactate retention rate after 0.45 μm filtration is 80.00-99.00%. After the functional water-soluble fertilizer is stored at 25-40℃ for 30-180 days under sealed packaging conditions, when it is formulated into an aqueous solution with a mass fraction of 10 wt%, the pH value is 5.30-7.00, and the water-insoluble matter content is not higher than 1.00 wt%.

[0016] As a concept of this invention, the present invention employs a design that combines a chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ionic complex with macro- and micronutrients. This design aims to achieve a synergistic balance between effective retention of functional components and stable dispersion in high-salt water-soluble systems. In existing technologies, to improve chitosan oligosaccharide lactate retention, polyelectrolyte complexation or multivalent ion binding is typically enhanced. However, excessively strong ion association can easily lead to flocculation, filtration loss, and increased water-insoluble matter. Conversely, improving dispersion stability often weakens the complexing effect or reduces the activity of multivalent nutrients, which is detrimental to the retention of chitosan oligosaccharide lactate and micronutrients in the fertilizer system. This invention, by limiting the mass ratio of chitosan oligosaccharide lactate to γ-polyglutamic acid potassium salt, the weakly acidic pH, the aqueous phase complexation, and the order of batch addition, allows ion complexation, buffer regulation, and nutrient salt compounding to mutually correct each other, thereby balancing dispersion stability, filtration retention, and water solubility in storage. Among them, the chitosan oligosaccharide lactate retention rate after 0.45μm filtration is used to characterize the change in chitosan oligosaccharide lactate content before and after filtration, and DLS and Zeta potential are used to characterize the water dispersion state of the composite system. The above indicators together serve as the basis for quality control of the composite system after entering the fertilizer formulation step or after the finished product is reconstituted.

[0017] This invention also discloses a method for preparing a functional water-soluble fertilizer containing chitosan oligosaccharide lactate, comprising the following steps: S1. Provides a pre-prepared aqueous dispersion of a chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ionic complex obtained by mixing and filtering chitosan oligosaccharide lactate aqueous solution and γ-polyglutamic acid potassium salt aqueous solution at a mass ratio of chitosan oligosaccharide lactate to γ-polyglutamic acid potassium salt of 1:0.50-4.00 at pH 5.20-6.80; S2. Add urea, potassium dihydrogen phosphate, potassium nitrate, magnesium sulfate heptahydrate, zinc sulfate heptahydrate, ferrous sulfate heptahydrate, boric acid, manganese sulfate monohydrate and ammonium molybdate tetrahydrate, and optionally calcium nitrate tetrahydrate to the aqueous dispersion of the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex to obtain a liquid mixture. S3. Using citric acid monohydrate and a potassium hydroxide aqueous solution with a mass concentration of 5.00-30.00wt%, the pH of the liquid mixture is adjusted to 5.50-6.80, followed by filtration, concentration and drying to obtain the functional water-soluble fertilizer.

[0018] Further, in step S2, urea, potassium dihydrogen phosphate, and potassium nitrate are added first, followed by magnesium sulfate heptahydrate, zinc sulfate heptahydrate, ferrous sulfate heptahydrate, boric acid, manganese sulfate monohydrate, and ammonium molybdate tetrahydrate. During the addition process, the temperature is controlled at 25-45℃ and the pH at 5.50-6.80. The ferrous sulfate heptahydrate is added after the zinc sulfate heptahydrate, boric acid, manganese sulfate monohydrate, ammonium molybdate tetrahydrate, and calcium nitrate tetrahydrate (if present). After adding the ferrous sulfate heptahydrate, stirring is continued for 20-60 minutes.

[0019] Furthermore, in step S3, the filtration is carried out using a 100-200 mesh filter, and the filtered solution is concentrated to obtain a solid content of 30.00-70.00 wt%; the concentrated solution is then spray-dried with an inlet air temperature of 120-180℃ and an outlet air temperature of 60-90℃ to obtain a solid functional water-soluble fertilizer with a moisture content of 0.50-5.00 wt%.

[0020] Furthermore, steps S1 to S3 are completed using an intermittent or continuous aqueous phase process. No organic solvents are used in steps S1 to S3. The pH of the material system in steps S1 to S3 is controlled online at 5.20-6.80. When the functional water-soluble fertilizer obtained after step S3 is formulated into an aqueous solution with a mass fraction of 10wt%, the pH value is 5.50-6.80 and the water-insoluble matter is 0.05-0.80wt%.

[0021] Furthermore, in preparing the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ionic complex, an aqueous solution of chitosan oligosaccharide lactate containing 1.00-15.00 wt% and an aqueous solution of γ-polyglutamic acid potassium salt containing 1.00-30.00 wt% are added to the same aqueous phase mixture at a mass ratio of chitosan oligosaccharide lactate to γ-polyglutamic acid potassium salt of 1:0.50-4.00 under an absolute pressure of 0.09-0.11 MPa and an air atmosphere. The temperature of the mixture is controlled at 25-45℃, the pH is controlled at 5.20-6.80, and the stirring time is controlled at 30-120 min. Subsequently, the mixture is filtered through a 100-200 mesh filter to obtain an aqueous dispersion of the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ionic complex for formulating functional water-soluble fertilizers.

[0022] Furthermore, the composite state of the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex aqueous dispersion was characterized as follows: The filtered chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex aqueous dispersion was used as the test sample. The test sample was diluted with deionized water to a composite mass fraction of 0.50 wt%. The hydrodynamic particle size, D90 and polydispersity index were recorded by dynamic light scattering at 25℃ and pH 5.50-6.50. The Zeta potential was recorded by electrophoretic light scattering. The system obtained by directly mixing chitosan oligosaccharide lactate and γ-polyglutamic acid potassium salt at the same mass ratio was used as the control system. The obtained particle size, polydispersity index and Zeta potential data were used for quality control of the composite aqueous dispersion before it entered the fertilizer preparation step. For the evaluation of the dispersibility of the reconstituted finished product, the sample of the functional water-soluble fertilizer prepared into an aqueous solution with a mass fraction of 10 wt% was used as the test sample. The particle size, polydispersity index and Zeta potential were recorded at the same temperature and pH, and the obtained data were used as the quality control data of the dispersion state of the reconstituted finished product.

[0023] Furthermore, the retention rate of chitosan oligosaccharide lactate after 0.45 μm filtration was determined as follows: A sample prepared as a 10 wt% aqueous solution of chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex or functional water-soluble fertilizer was used as the test sample. The sample was filtered through a 0.45 μm aqueous filter membrane at 25 °C. The chitosan oligosaccharide lactate content in the sample before filtration and in the filtrate were measured separately. The retention rate was calculated as: (Mass of chitosan oligosaccharide lactate in the filtrate / Mass of chitosan oligosaccharide lactate in the sample before filtration) × 100%, and the calculation result was used as the quality control data for the filtration stability of the complex. For samples without chitosan oligosaccharide lactate, the retention rate of chitosan oligosaccharide lactate was not calculated.

[0024] Furthermore, the molecular weights of γ-polyglutamic acid raw materials and chitosan oligosaccharide lactate raw materials were determined by gel permeation chromatography. The test samples were dissolved in a 0.1 mol / L sodium nitrate aqueous solution and filtered through a 0.45 μm aqueous filter membrane before injection. Dextran was used as the calibration standard. The mobile phase was a 0.1 mol / L sodium nitrate aqueous solution, and the column temperature was 35 °C. The number-average molecular weight, weight-average molecular weight, and molecular weight distribution were recorded. The obtained molecular weight data were used as the raw material release data for the preparation steps of γ-polyglutamic acid potassium salt aqueous solution and chitosan oligosaccharide lactate aqueous solution.

[0025] Furthermore, the degree of carboxyl potassium salt concentration in the γ-polyglutamic acid potassium salt aqueous solution was determined by potentiometric titration. The dried sample of the γ-polyglutamic acid potassium salt aqueous solution was used as the test sample. The total molar number of carboxyl groups and the free molar number of γ-polyglutamic acid were measured respectively. The degree of carboxyl potassium salt concentration was calculated as: total molar number of carboxyl groups minus free molar number of carboxyl groups, then divided by the total molar number of carboxyl groups and multiplied by 100%. The calculation result was used as the quality control data before the γ-polyglutamic acid potassium salt aqueous solution entered the chitosan oligosaccharide lactate compounding step.

[0026] Furthermore, the pH value of the functional water-soluble fertilizer is determined as follows: 10.00 parts by weight of solid functional water-soluble fertilizer is added to 90.00 parts by weight of deionized water and stirred at 25°C for 30 minutes to obtain an aqueous solution with a mass fraction of 10 wt%. The pH electrode is placed in the aqueous solution to read the pH value, and this pH value is used as the quality control data for the acidity and alkalinity of the finished aqueous solution.

[0027] Further, magnesium sulfate heptahydrate, zinc sulfate heptahydrate, ferrous sulfate heptahydrate, boric acid, manganese sulfate monohydrate, and ammonium molybdate tetrahydrate are prepared into aqueous solutions with a mass concentration of 1.00-30.00 wt% and then added. During addition, the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex aqueous dispersion is first mixed with urea, potassium dihydrogen phosphate, and potassium nitrate to form a basic mixture. Then, each aqueous solution is added in batches at 25-45℃ and pH 5.50-6.80, with each batch added for 5-30 minutes, and the total addition time is 30-120 minutes. The ferrous sulfate heptahydrate aqueous solution is added after the zinc sulfate heptahydrate aqueous solution, boric acid aqueous solution, manganese sulfate monohydrate aqueous solution, and ammonium molybdate tetrahydrate aqueous solution. After the addition is completed, stirring is continued for 20-60 minutes. The resulting mixture is then subjected to filtration, concentration, and drying steps. The order in which the ferrous sulfate heptahydrate aqueous solution is added is used to reduce its local contact time during the batch compounding process of trace elements, and the water-insoluble matter after the addition, the filtration state, and the water-insoluble matter after storage are used as process control indicators.

[0028] Furthermore, when the functional water-soluble fertilizer includes calcium nitrate tetrahydrate, the calcium nitrate tetrahydrate is prepared into an aqueous solution with a mass concentration of 1.00-30.00 wt%, and added in batches to an aqueous mixture containing chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex, urea, potassium dihydrogen phosphate, and potassium nitrate. During the addition process, the temperature is controlled at 25-45℃, the pH is controlled at 5.50-6.80, and the addition time for each batch is 5-30 minutes. After the addition is completed, stirring is continued for 20-60 minutes. The resulting calcium-containing mixture then proceeds to the filtration, concentration, and drying steps. The calcium nitrate tetrahydrate aqueous solution is added before the ferrous sulfate heptahydrate aqueous solution. The condition for the mixture to proceed to the filtration step is that there is no visible precipitate and the water-insoluble matter is not higher than 0.80 wt%.

[0029] Furthermore, during the spray drying of the concentrate, the solid content of the filtered concentrate was controlled to be 30.00-70.00 wt%, the inlet air temperature of the spray drying equipment was controlled to be 120-180℃, and the outlet air temperature was controlled to be 60-90℃. The resulting powder was collected and stored under sealed packaging conditions. The resulting powder was used to prepare a 10 wt% aqueous solution and the pH value, water-insoluble matter, and chitosan oligosaccharide lactate retention rate were tested. The solid content of the concentrate before spray drying, the inlet air temperature, the outlet air temperature, and the moisture content of the resulting powder were used as quality control parameters for the drying process.

[0030] As another aspect of this invention, the present invention employs a pre-prepared ionic complex aqueous dispersion followed by the stepwise addition of nutrients, pH adjustment, filtration, concentration, and drying. This process is primarily used to achieve, fix, or amplify the aforementioned synergistic effects. Existing technologies, if chitosan oligosaccharide lactate, polyglutamate, and high-concentration fertilizer salts are directly mixed at once, are prone to flocculation or precipitation due to excessively high local ionic strength and instantaneous contact of polyvalent metal ions. Simply reducing the activity of the nutrients would weaken the supply of micronutrients. This invention first forms an ionic complex under controlled pH and temperature, then adds macronutrients and micronutrients sequentially, and adjusts the acid-base state using citric acid monohydrate and potassium hydroxide aqueous solution. This ensures the composite structure remains dispersible during fertilizer preparation and drying, thereby achieving a synergistic effect of functional component retention and fertilizer storage stability.

[0031] Chitosan oligosaccharide lactate is primarily designed for the retention of functional oligosaccharides and their bioactivity in plants, while γ-polyglutamic acid potassium salt is mainly designed for aqueous dispersion, ion buffering, and compatibility with nutrient systems. While chitosan oligosaccharide lactate, when present alone or in a high proportion, can increase the input of functional components, it is prone to increased filtration losses due to local association in high-salt and polyvalent metal ion environments. Similarly, while γ-polyglutamic acid potassium salt, when present alone or in a high proportion, is beneficial for dispersion and complexation buffering, it may weaken the effective loading of chitosan oligosaccharide lactate and alter the system viscosity. This invention, through the control of their mass ratio, weakly acidic pH, controlled temperature, and batch addition sequence, enables the cationic chitosan oligosaccharide lactate and the anionic γ-polyglutamic acid potassium salt to form a filterable ionic complex, buffering the precipitation tendency during the addition of trace elements, ultimately balancing dispersion stability with the effective retention of chitosan oligosaccharide lactate.

[0032] Beneficial technical effects 1. This invention forms an ionic complex between chitosan oligosaccharide lactate and γ-polyglutamic acid potassium salt, so that chitosan oligosaccharide lactate does not exist in a single free state in a high-salt water fertilizer system. This reduces the risk of loss of functional components during filtration and takes into account both stable dispersion and effective retention in the aqueous phase.

[0033] 2. This invention combines urea, potassium dihydrogen phosphate, potassium nitrate, and nutrients such as magnesium, zinc, iron, boron, manganese, and molybdenum in batches under a weakly acidic pH. This process controls the reactivity of polyvalent metal ions, reduces the risk of visible precipitation and increased water-insoluble matter, and improves storage and application stability.

[0034] 3. This invention uses citric acid monohydrate and potassium hydroxide aqueous solution to adjust the pH of the system, so that chitosan oligosaccharide lactate, γ-polyglutamic acid potassium salt and various fertilizer salts are within the compatibility window, avoiding the deterioration of dispersion caused by simply enhancing ion binding, and forming a water-soluble fertilizer system that is more suitable for drip irrigation, fertigation and foliar spraying.

[0035] 4. This invention pre-prepares an aqueous dispersion of ionic complexes, then adds nutrients, filters, concentrates, and spray-dries them, so that the complex state is maintained in the finished powder, making it easy to form a solid functional water-soluble fertilizer that can be compounded, packaged, transported, and quickly prepared into a 10wt% aqueous solution.

[0036] 5. This invention sets out quality control items such as DLS / Zeta, chitosan oligosaccharide lactate retention rate after 0.45μm filtration, GPC molecular weight, carboxyl potassium salting degree, water-insoluble matter, and pH after storage, so that the functional component status, filtration stability, and storage water solubility of the product can be quantitatively evaluated, which is beneficial for reproducibility and quality release. Attached Figure Description

[0037] Figure 1 The graph shows the effect of complex content on chitosan oligosaccharide lactate retention and water-insoluble matter. Figure 2 The graph shows the effect of the composite mass ratio on the retention rate of chitosan oligosaccharide lactate and the D90 of the composite. Figure 3 Figure showing the effect of compound pH on chitosan oligosaccharide lactate retention and water-insoluble matter; Figure 4 Figure 1 shows the effect of spray drying inlet air temperature on chitosan oligosaccharide lactate retention rate and finished product moisture content. Figure 5 The DLS differential particle size distribution diagrams for Example 1, Comparative Example 8, and Comparative Example 10 are shown. Figure 6 The cumulative particle size distribution of DLS in Example 1, Comparative Example 8, and Comparative Example 10 are shown. Figure 7 The Zeta potential distribution diagrams for Example 1, Comparative Example 8, and Comparative Example 9 are shown. Figure 8 Paired graphs showing the chitosan oligosaccharide lactate content before and after filtration in Examples 1, 8, and 10. Figure 9 Scatter plot of chitosan oligosaccharide lactate filtration retention rate for Example 1, Comparative Example 8, and Comparative Example 10; Figure 10 The graph shows the changes in water-insoluble matter during the storage process of Examples 1, 5, and 6. Figure 11 Here are the pH drift diagrams for Example 1, Comparative Example 5, and Comparative Example 6 during storage; Figure 12 GPC / SEC molecular weight distribution of chitosan oligosaccharide lactate and γ-polyglutamic acid potassium salt; Figure 13 First derivative plot of carboxyl potassium salt titration of γ-polyglutamic acid potassium salt; Figure 14This is a comparison of macroscopic optical photographs of the final product of Example 1 and the final product of Comparative Example 10. Figure 15 This is a comparison of the SEM morphology of the final product of Example 1 and the final product of Comparative Example 10; Figure 16 This is a macroscopic optical photographic evolution diagram of S1 to the final product in Example 1. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0039] Example 1 This embodiment prepares 1000.00g of powdered functional water-soluble fertilizer. The finished product contains 2.00g of chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex, 50.00g of urea, 600.00g of potassium dihydrogen phosphate, 339.59g of potassium nitrate, 2.00g of magnesium sulfate heptahydrate, 0.50g of zinc sulfate heptahydrate, 0.50g of ferrous sulfate heptahydrate, 0.20g of boric acid, 0.10g of manganese sulfate monohydrate, 0.01g of ammonium molybdate tetrahydrate, 0.10g of citric acid monohydrate, and 5.00g of water. All the above raw materials are commercially available or purchased grade raw materials. Urea, potassium dihydrogen phosphate, and potassium nitrate are water-soluble fertilizer grade, while magnesium sulfate heptahydrate, zinc sulfate heptahydrate, ferrous sulfate heptahydrate, boric acid, manganese sulfate monohydrate, ammonium molybdate tetrahydrate, and citric acid monohydrate are fertilizer grade or analytical grade. The conductivity of deionized water is not higher than 10μS / cm.

[0040] S1: Preparation of γ-polyglutamic acid potassium salt aqueous solution. Weigh 100.00 g of γ-polyglutamic acid and add it to 3000.00 g of deionized water. Stir mechanically at 20℃ for 0.5 h at a stirring speed of 300 rpm to obtain a γ-polyglutamic acid hydrate. Add a 5.00 wt% potassium hydroxide aqueous solution dropwise to this hydrate, maintaining the temperature at 20℃ and the pH at 6.50 during the addition. Continue stirring for 0.5 h. Stop the neutralization adjustment when the pH change does not exceed 0.20 within 30 min. Filter the solution through a 100-mesh sieve and adjust with water to obtain a γ-polyglutamic acid potassium salt aqueous solution with a solid content of 1.00 wt% and a carboxyl potassium salt concentration of 70.00 mol%.

[0041] S2: Preparation of chitosan oligosaccharide lactate aqueous solution. Weigh 100.00 g of chitosan oligosaccharide lactate with a number average molecular weight of 300 Da, add it to 10000.00 g of deionized water, and stir for 20 min at 300 rpm under an atmosphere of 20℃, 0.09 MPa absolute pressure, and air to obtain a crude chitosan oligosaccharide lactate solution. Adjust the pH to 4.80 using citric acid monohydrate and a 5.00 wt% potassium hydroxide aqueous solution, and filter through a 100-mesh sieve to obtain a chitosan oligosaccharide lactate aqueous solution containing 1.00 wt% chitosan oligosaccharide lactate and no more than 1.00 wt% water-insoluble matter.

[0042] S3: Preparation of an aqueous dispersion of chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ionic complex. Chitosan oligosaccharide lactate and γ-polyglutamic acid potassium salt were added at a mass ratio of 1:0.50, with 1.333 g of chitosan oligosaccharide lactate and 0.667 g of γ-polyglutamic acid potassium salt. The corresponding amounts of the two aqueous solutions were added to the same aqueous phase mixture. The mixture was stirred for 30 min at 25°C, 0.09 MPa absolute pressure, and air atmosphere. The pH of the system was controlled at 5.20, and the stirring speed was 400 rpm. When the pH change did not exceed 0.20 within 30 min, and no flocculent matter was retained after filtration through a 100 μm sieve, the mixture was filtered through a 100-mesh sieve to obtain the aqueous dispersion of chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ionic complex. The aqueous dispersion of the ionic complex in this embodiment can be dried at 45°C for 2 h to obtain a solid ionic complex sample for quality testing.

[0043] S4: Preparation of fertilizer mixture. The aqueous dispersion of the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex of this embodiment was added to the mixing tank and stirred at 25°C under an air atmosphere. Urea 50.00g, potassium dihydrogen phosphate 600.00g, and potassium nitrate 339.59g were added sequentially, and the mixture was stirred for 30 minutes until the system was clear or free of visible undissolved particles. Magnesium sulfate heptahydrate, zinc sulfate heptahydrate, boric acid, manganese sulfate monohydrate, ammonium molybdate tetrahydrate, and ferrous sulfate heptahydrate were each prepared into 1.00wt% aqueous solutions and added sequentially in batches. The ferrous sulfate heptahydrate aqueous solution was added after the zinc sulfate heptahydrate, boric acid, manganese sulfate monohydrate, and ammonium molybdate tetrahydrate aqueous solutions. Each batch was added over 5 minutes, for a total addition time of 30 minutes. The pH was controlled at 5.50 during the addition process.

[0044] S5: Filtration, concentration, and drying. After addition, continue stirring for 20 minutes at a stirring speed of 400 rpm. The endpoint is when there is no visible precipitate in the mixture and the water-insoluble matter is no more than 0.80 wt%. Filter the mixture through a 100-mesh sieve. After filtration, concentrate under reduced pressure at below 55°C to a solid content of 30.00 wt%. Then, spray dry the mixture at an inlet air temperature of 120°C and an outlet air temperature of 60°C. Collect the powder and store it in sealed packaging to obtain the functional water-soluble fertilizer of this embodiment.

[0045] Quality testing methods and results: 10.00g of the solid functional water-soluble fertilizer of this embodiment was added to 90.00g of deionized water and stirred at 25℃ for 30min to obtain an aqueous solution with a mass fraction of 10wt%, and the pH was measured to be 5.50; the water-insoluble matter was determined to be 0.12wt% using the water-insoluble matter determination method; the chitosan oligosaccharide lactate content before and after filtration through a 0.45μm filter membrane was determined to be 86.20%; after diluting the aqueous dispersion of the ion complex to a complex mass fraction of 0.50wt%, the D90 was measured to be 220nm, the polydispersity index was 0.31, and the Zeta potential was +8.5mV.

[0046] Features and application scenarios of this embodiment: This embodiment adopts milder compound and dry conditions, with functional ionic complexes, trace elements and moisture in low value ranges, and potassium dihydrogen phosphate in high value ranges. It is suitable for drip irrigation, fertigation and foliar spraying scenarios that focus on phosphorus and potassium nutrient supply and low water-insoluble matter control.

[0047] Example 2 Raw materials and proportions: This embodiment prepares 1000.00g of calcium-containing powdered functional water-soluble fertilizer. The finished product contains 50.00g of chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex, 400.00g of urea, 100.00g of potassium dihydrogen phosphate, 246.00g of potassium nitrate, 80.00g of magnesium sulfate heptahydrate, 30.00g of zinc sulfate heptahydrate, 30.00g of ferrous sulfate heptahydrate, 30.00g of boric acid, 10.00g of manganese sulfate monohydrate, 2.00g of ammonium molybdate tetrahydrate, 15.00g of citric acid monohydrate, 2.00g of calcium nitrate tetrahydrate, and 5.00g of water. The mass ratio of calcium nitrate tetrahydrate to potassium dihydrogen phosphate is 0.02:1. All the above raw materials are commercially available or purchased. γ-Polyglutamic acid is a fertilizer-grade or fermentation-derived commercially available raw material, and chitosan oligosaccharide lactate has a number-average molecular weight of 5000 Da.

[0048] Preparation of γ-polyglutamic acid potassium salt aqueous solution: 100.00 g of γ-polyglutamic acid was added to 300.00 g of deionized water and mechanically stirred at 40 °C for 2.0 h at a stirring speed of 600 rpm to obtain γ-polyglutamic acid hydrate. A 30.00 wt% potassium hydroxide aqueous solution was added dropwise to the hydrate, with the temperature controlled at 40 °C and the pH controlled at 8.00 during the dropwise addition. Stirring was continued for 2.0 h. Neutralization and adjustment were ended when the pH change did not exceed 0.20 within 30 min. The solution was filtered through a 200-mesh sieve and concentrated to obtain a γ-polyglutamic acid potassium salt aqueous solution with a solid content of 30.00 wt% and a carboxyl potassium salt concentration of 100.00 mol%.

[0049] Preparation of chitosan oligosaccharide lactate aqueous solution: 100.00 g of chitosan oligosaccharide lactate was added to 600.00 g of deionized water and stirred for 60 min at 40℃ and 0.11 MPa absolute pressure, with a stirring speed of 600 rpm, to obtain a crude chitosan oligosaccharide lactate solution; the pH was adjusted to 6.50 using citric acid monohydrate and a 30.00 wt% potassium hydroxide aqueous solution, and then filtered through a 200-mesh filter and concentrated to obtain a chitosan oligosaccharide lactate aqueous solution containing 15.00 wt% chitosan oligosaccharide lactate.

[0050] Preparation process: Chitosan oligosaccharide lactate and γ-polyglutamic acid potassium salt were added at a mass ratio of 1:4.00, with 10.00 g of chitosan oligosaccharide lactate and 40.00 g of γ-polyglutamic acid potassium salt. The corresponding amounts of the two aqueous solutions were added to a composite tank and stirred for 120 min at 45℃, 0.11 MPa absolute pressure and air atmosphere. The pH was controlled at 6.80 and the stirring speed was 600 rpm. After the pH change did not exceed 0.20 within 30 min and no flocculent residue was retained after filtration through a 100 μm sieve, the mixture was filtered through a 200 mesh to obtain an aqueous dispersion of chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex. The aqueous dispersion was mixed with urea, potassium dihydrogen phosphate, and potassium nitrate at 45°C for 30 min. Then, magnesium sulfate heptahydrate, zinc sulfate heptahydrate, boric acid, manganese sulfate monohydrate, ammonium molybdate tetrahydrate, calcium nitrate tetrahydrate, and ferrous sulfate heptahydrate were prepared into aqueous solutions with a mass concentration of 30.00 wt% and added in batches. The ferrous sulfate heptahydrate aqueous solution was added after the zinc sulfate heptahydrate aqueous solution, boric acid aqueous solution, manganese sulfate monohydrate aqueous solution, ammonium molybdate tetrahydrate aqueous solution, and calcium nitrate tetrahydrate aqueous solution. Each batch was added over a period of 30 min, and the total addition time was 120 min. The pH of the system was controlled at 6.80.

[0051] Post-processing: After the batch addition was completed, stirring continued for 60 minutes until the mixture showed no visible precipitate and the water-insoluble matter content was no higher than 0.80 wt%. The mixture was filtered through a 200-mesh sieve and concentrated to a solid content of 70.00 wt%. It was then spray-dried at an inlet air temperature of 180℃ and an outlet air temperature of 90℃. The powder was collected and stored in sealed packaging. Separately, an aqueous dispersion of the ion complex was dried at 75℃ for 8 hours to obtain a solid ion complex sample for quality testing.

[0052] Quality testing methods and results: After the solid functional water-soluble fertilizer of this embodiment was prepared into an aqueous solution with a mass fraction of 10 wt%, the pH was measured to be 6.80 at 25℃, and the water-insoluble matter was 0.62 wt%. After filtration at 0.45 μm, the chitosan oligosaccharide lactate retention rate was 95.60%. After diluting the ionic complex aqueous dispersion to 0.50 wt%, the D90 was measured to be 480 nm, the polydispersity index was 0.42, and the Zeta potential was -12.3 mV. After being sealed and stored at 40℃ for 180 days, it was prepared into an aqueous solution with a mass fraction of 10 wt%, and the pH was measured to be 6.92, and the water-insoluble matter was 0.88 wt%.

[0053] The features of this embodiment are: This embodiment adopts a high-load functional complex, micronutrient and urea formula, and uses high temperature, long compounding time and high solid content concentration and drying conditions, which is suitable for high nutrient compound water-soluble fertilizers that require high input of functional components and supply of micronutrients.

[0054] Example 3 In this embodiment, the preparation scale is 1000.00g, and the product form is a solid powder containing calcium nitrate tetrahydrate. The finished product formula is as follows: 15.00g of chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex, 262.50g of urea, 100.00g of potassium dihydrogen phosphate, 500.00g of potassium nitrate, 20.00g of magnesium sulfate heptahydrate, 5.00g of zinc sulfate heptahydrate, 5.00g of ferrous sulfate heptahydrate, 5.00g of boric acid, 2.00g of manganese sulfate monohydrate, 0.50g of ammonium molybdate tetrahydrate, 5.00g of citric acid monohydrate, 50.00g of water, and 30.00g of calcium nitrate tetrahydrate. The mass ratio of calcium nitrate tetrahydrate to potassium dihydrogen phosphate is 0.30:1.

[0055] Key parameters are listed below: the mass ratio of chitosan oligosaccharide lactate to γ-polyglutamic acid potassium salt is 1:2.00, with 5.00g of chitosan oligosaccharide lactate and 10.00g of γ-polyglutamic acid potassium salt; the aqueous solution of chitosan oligosaccharide lactate contains 8.00wt% chitosan oligosaccharide lactate; the aqueous solution of γ-polyglutamic acid potassium salt contains 20.00wt% γ-polyglutamic acid potassium salt; the composite pH is 6.00, the composite temperature is 35℃, the composite time is 75min, the composite pressure is 0.10MPa absolute pressure, and filtration is performed using a 150-mesh filter; the solid content of the concentrated liquid is 55.00wt%, the spray drying inlet air temperature is 150℃, and the outlet air temperature is 75℃.

[0056] In the preparation process, 100.00g of γ-polyglutamic acid was first added to 1200.00g of deionized water and stirred at 30℃ for 1.0h at a stirring speed of 500rpm. A potassium hydroxide aqueous solution with a mass concentration of 15.00wt% was added dropwise to the resulting hydrated solution. The temperature was controlled at 30℃ and the pH was controlled at 7.20. Stirring was continued for 1.0h. When the pH change did not exceed 0.20 within 30min, the neutralization and adjustment were terminated. The solution was filtered through a 150-mesh filter and concentrated to obtain a potassium γ-polyglutamic acid aqueous solution with a solid content of 20.00wt% and a carboxyl potassium salt concentration of 85.00mol%. Separately, 100.00 g of chitosan oligosaccharide lactate with a number average molecular weight of 1200 Da was added to 3000.00 g of deionized water and stirred for 40 min at 30 °C and 0.10 MPa absolute pressure. The pH was adjusted to 5.80 with citric acid monohydrate and potassium hydroxide aqueous solution with a mass concentration of 15.00 wt%. After filtration through 150 mesh and concentration adjustment, an aqueous solution of chitosan oligosaccharide lactate was obtained.

[0057] Subsequently, the two aqueous solutions were added to a composite tank at a predetermined mass ratio and stirred for 75 min under air atmosphere, 35℃, and absolute pressure of 0.10 MPa. The pH of the system was controlled at 6.00, and the stirring speed was 500 rpm. After reaching a state where the pH change did not exceed 0.20 within 30 min and no flocculent residue was retained after filtration through a 100 μm sieve, the mixture was filtered through a 150 mesh to obtain an aqueous dispersion of chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex. This aqueous dispersion was mixed with urea, potassium dihydrogen phosphate, and potassium nitrate to form a basic mixture. Then, magnesium sulfate heptahydrate, zinc sulfate heptahydrate, boric acid, manganese sulfate monohydrate, ammonium molybdate tetrahydrate, calcium nitrate tetrahydrate, and ferrous sulfate heptahydrate were prepared into aqueous solutions with a mass concentration of 15.00 wt%. These solutions were added in batches at 35℃ and pH 6.20, with each batch added over 20 min, for a total addition time of 90 min. The ferrous sulfate heptahydrate aqueous solution was added last.

[0058] After adding the ingredients, continue stirring for 45 minutes. Once no visible precipitate remains in the mixture, filter through a 150-mesh screen and concentrate to a solid content of 55.00 wt%. Then, spray dry to obtain a solid functional water-soluble fertilizer with a moisture content of 5.00 wt%. Separately, take an aqueous dispersion of the ion complex and dry it at 60℃ for 5 hours. The resulting solid ion complex is used for testing water-insoluble matter and filtration retention rate.

[0059] Quality testing methods and results: After the solid functional water-soluble fertilizer of this embodiment was prepared into a 10wt% aqueous solution, the pH was measured to be 6.20 at 25℃, and the water-insoluble matter was 0.45wt%; after 0.45μm filtration, the chitosan oligosaccharide lactate retention rate was 92.40%; the D90 of the complex aqueous dispersion was measured to be 310nm, the polydispersity index was 0.36, and the Zeta potential was -4.6mV by DLS; after being stored in sealed packaging at 40℃ for 180 days, it was prepared into a 10wt% aqueous solution with a pH of 6.45 and a water-insoluble matter of 0.78wt%.

[0060] Applicable scenarios for this embodiment: This embodiment adopts a high potassium, calcium and high moisture control scheme, which is suitable for fruit and vegetable crops, facility cultivation and drip irrigation water-soluble fertilizers that have high requirements for synergistic potassium and calcium supplementation and powder solubility.

[0061] Example 4 I. Preparation Object and Finished Product Formula: Using 1000.00g of solid functional water-soluble fertilizer as the preparation object, the finished product contains 30.00g of chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex, 400.00g of urea, 387.00g of potassium dihydrogen phosphate, 50.00g of potassium nitrate, 40.00g of magnesium sulfate heptahydrate, 10.00g of zinc sulfate heptahydrate, 10.00g of ferrous sulfate heptahydrate, 10.00g of boric acid, 4.00g of manganese sulfate monohydrate, 1.00g of ammonium molybdate tetrahydrate, 8.00g of citric acid monohydrate, and 50.00g of water. All raw materials are commercially available or purchased grade. The powdered raw materials were inspected through a 100-mesh sieve before use and showed no obvious mechanical impurities.

[0062] II. Preparation of composite raw material solution: 100.00g of γ-polyglutamic acid was added to 800.00g of deionized water and stirred at 25℃ for 1.5h at a stirring speed of 450rpm. A potassium hydroxide aqueous solution with a mass concentration of 10.00wt% was added dropwise. During the dropwise addition, the temperature was controlled at 25℃ and the pH was controlled at 7.00. Stirring was continued for 1.5h. After filtration through a 150-mesh filter and concentration adjustment, a potassium hydroxide aqueous solution of γ-polyglutamic acid with a solid content of 15.00wt% and a carboxyl potassium salt concentration of 80.00mol% was obtained. 100.00 g of chitosan oligosaccharide lactate with a number average molecular weight of 2500 Da was added to 1500.00 g of deionized water and stirred for 30 min at 25 °C and 0.10 MPa absolute pressure. The pH was adjusted to 5.20 with citric acid monohydrate and 10.00 wt% potassium hydroxide aqueous solution. After filtration through 150 mesh and concentration adjustment, an aqueous solution of chitosan oligosaccharide lactate with a content of 12.00 wt% was obtained.

[0063] III. Ion Complexation and Basic Mixing: 12.00 g of chitosan oligosaccharide lactate and 18.00 g of γ-polyglutamic acid potassium salt were added to a complexing tank at a mass ratio of 1:1.50. The mixture was stirred for 60 min at 30℃, 0.10 MPa absolute pressure, and in air atmosphere. The pH was controlled at 5.60, and the stirring speed was 450 rpm. After checking for no flocculent residue through a 100 μm sieve, the mixture was filtered through a 150-mesh sieve to obtain an aqueous dispersion of the ion complex. This aqueous dispersion was then mixed with urea, potassium dihydrogen phosphate, and potassium nitrate, and stirred for 30 min to form a basic mixture.

[0064] IV. Addition and Drying of Trace Elements: Prepare aqueous solutions of magnesium sulfate heptahydrate, zinc sulfate heptahydrate, boric acid, manganese sulfate monohydrate, ammonium molybdate tetrahydrate, and ferrous sulfate heptahydrate, each with a mass concentration of 10.00 wt%. Add these solutions in batches to the base mixture at 30℃ and pH 5.90, with each batch added over 15 minutes, for a total addition time of 60 minutes. The ferrous sulfate heptahydrate aqueous solution is added after the zinc sulfate heptahydrate, boric acid, manganese sulfate monohydrate, and ammonium molybdate tetrahydrate aqueous solutions. After addition, continue stirring for 30 minutes. Filter the solution through a 150-mesh sieve and concentrate the filtrate to a solid content of 45.00 wt%. Spray dry the solution at an inlet air temperature of 140℃ and an outlet air temperature of 70℃. Collect the powder and seal it in packaging.

[0065] V. Quality Testing Methods and Results: 10.00g of the powder from this embodiment was added to 90.00g of deionized water and stirred at 25℃ for 30min. The pH of the 10wt% aqueous solution was measured to be 5.90, and the water-insoluble matter was 0.38wt%. After filtration at 0.45μm, the chitosan oligosaccharide lactate retention rate was 90.10%. The D90 of the complex aqueous dispersion was 360nm, the polydispersity index was 0.34, and the Zeta potential was +1.7mV. After being sealed and stored at 30℃ for 90d, the pH of the 10wt% aqueous solution was 6.05, and the water-insoluble matter was 0.63wt%.

[0066] VI. Process characteristics and application direction of this embodiment: This embodiment adopts a combination of high urea, low potassium nitrate and medium intensity composite process. The structure of macro elements and the order of addition of micro elements in the formula are coordinated, which is suitable for general functional water-soluble fertilizers that require high nitrogen supply and take into account weak acid water solubility and stability.

[0067] Comparative Example 1: Basically the same as Example 1, except that the content of the finished product of chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex is 0.10 wt%, and potassium nitrate is used to make up the total mass of the finished product to 100 wt%. Other conditions are maintained as follows: urea 5.00 wt%, potassium dihydrogen phosphate 60.00 wt%, magnesium sulfate heptahydrate 0.20 wt%, zinc sulfate heptahydrate 0.05 wt%, ferrous sulfate heptahydrate 0.05 wt%, boric acid 0.02 wt%, manganese sulfate monohydrate 0.01 wt%, ammonium molybdate tetrahydrate 0.001 wt%, citric acid monohydrate 0.01 wt%, water 0.50 wt%, chitosan oligosaccharide lactate to γ-polyglutamic acid potassium salt mass ratio 1:0.50, compound pH 5.20, compound temperature 25℃, compound time 30 min, absolute pressure 0.09 MPa air atmosphere, 100 mesh filtration, spray drying inlet air temperature 120℃ and outlet air temperature 60℃.

[0068] Comparative Example 2: Basically the same as Example 1, except that the mass ratio of chitosan oligosaccharide lactate to γ-polyglutamic acid potassium salt was adjusted to 1:0.20, the content of the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ionic complex was kept at 0.20 wt%, and other conditions were kept as follows: urea 5.00 wt%, potassium dihydrogen phosphate 60.00 wt%, potassium nitrate 33.959 wt%, magnesium sulfate heptahydrate 0.20 wt%, zinc sulfate heptahydrate 0.05 wt%, ferrous sulfate heptahydrate 0.05 wt%, boric acid 0.02 wt%, manganese sulfate monohydrate 0.01 wt%, ammonium molybdate tetrahydrate 0.001 wt%, citric acid monohydrate 0.01 wt%, moisture 0.50 wt%, composite pH 5.20, composite temperature 25℃, composite time 30 min, absolute pressure 0.09 MPa air atmosphere, 100 mesh filter, spray drying inlet air temperature 120℃ and outlet air temperature 60℃.

[0069] Comparative Example 3: Basically the same as Example 1, except that the composite pH in step A2 was controlled at 7.30, and other conditions were maintained as follows: 0.20 wt% chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex, 5.00 wt% urea, 60.00 wt% potassium dihydrogen phosphate, 33.959 wt% potassium nitrate, 0.20 wt% magnesium sulfate heptahydrate, 0.05 wt% zinc sulfate heptahydrate, 0.05 wt% ferrous sulfate heptahydrate, 0.02 wt% boric acid, 0.01 wt% manganese sulfate monohydrate, 0.001 wt% ammonium molybdate tetrahydrate, 0.01 wt% citric acid monohydrate, 0.50 wt% moisture, chitosan oligosaccharide lactate to γ-polyglutamic acid potassium salt mass ratio 1:0.50, composite temperature 25℃, composite time 30 min, absolute pressure 0.09 MPa air atmosphere, 100 mesh filtration, spray drying inlet air temperature 120℃ and outlet air temperature 60℃.

[0070] Comparative Example 4: Basically the same as Example 1, except that the mixing time in step A2 was 15 min, and other conditions were maintained as follows: 0.20 wt% chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex, 5.00 wt% urea, 60.00 wt% potassium dihydrogen phosphate, 33.959 wt% potassium nitrate, 0.20 wt% magnesium sulfate heptahydrate, 0.05 wt% zinc sulfate heptahydrate, 0.05 wt% ferrous sulfate heptahydrate, 0.02 wt% boric acid, 0.01 wt% manganese sulfate monohydrate, 0.001 wt% ammonium molybdate tetrahydrate, 0.01 wt% citric acid monohydrate, 0.50 wt% moisture, chitosan oligosaccharide lactate to γ-polyglutamic acid potassium salt mass ratio 1:0.50, composite pH 5.20, composite temperature 25℃, absolute pressure 0.09 MPa air atmosphere, 100 mesh filter, spray drying inlet air temperature 120℃ and outlet air temperature 60℃.

[0071] Comparative Example 5: Essentially the same as Example 1, except that the ferrous sulfate heptahydrate aqueous solution was added before the zinc sulfate heptahydrate aqueous solution, boric acid aqueous solution, manganese sulfate monohydrate aqueous solution, and ammonium molybdate tetrahydrate aqueous solution. Other conditions remained the same: the final product contained 0.20 wt% chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex, 5.00 wt% urea, 60.00 wt% potassium dihydrogen phosphate, 33.959 wt% potassium nitrate, 0.20 wt% magnesium sulfate heptahydrate, and 0.05 wt% zinc sulfate heptahydrate. The composition of the product is as follows: 0.05 wt% ferrous sulfate heptahydrate, 0.02 wt% boric acid, 0.01 wt% manganese sulfate monohydrate, 0.001 wt% ammonium molybdate tetrahydrate, 0.01 wt% citric acid monohydrate, 0.50 wt% water, compound pH 5.20, compound temperature 25℃, compound time 30 min, batch addition time 5 min, total addition time 30 min, stirring for 20 min after addition, 100 mesh filtration, spray drying inlet air temperature 120℃ and outlet air temperature 60℃.

[0072] Comparative Example 6: Basically the same as Example 1, except that when the finished product was prepared into a 10wt% aqueous solution, the pH was adjusted to 7.30, and other conditions were maintained as follows: 0.20wt% chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex, 5.00wt% urea, 60.00wt% potassium dihydrogen phosphate, 33.959wt% potassium nitrate, 0.20wt% magnesium sulfate heptahydrate, 0.05wt% zinc sulfate heptahydrate, 0.05wt% ferrous sulfate heptahydrate, 0.02wt% boric acid, 0.01wt% manganese sulfate monohydrate, 0.001wt% ammonium molybdate tetrahydrate, 0.01wt% citric acid monohydrate, 0.50wt% water, chitosan oligosaccharide lactate to γ-polyglutamic acid potassium salt mass ratio 1:0.50, composite pH 5.20, composite temperature 25℃, composite time 30min, absolute pressure 0.09MPa air atmosphere, 100-mesh filtration, spray drying inlet air temperature 120℃ and outlet air temperature 60℃.

[0073] Comparative Example 7: Basically the same as Example 1, except that the moisture content of the finished product is 7.00 wt%, and the potassium nitrate content is reduced accordingly to maintain the total mass of the finished product at 100 wt%. Other conditions are maintained as follows: 0.20 wt% chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex, 5.00 wt% urea, 60.00 wt% potassium dihydrogen phosphate, 0.20 wt% magnesium sulfate heptahydrate, 0.05 wt% zinc sulfate heptahydrate, 0.05 wt% ferrous sulfate heptahydrate, 0.02 wt% boric acid, 0.01 wt% manganese sulfate monohydrate, 0.001 wt% ammonium molybdate tetrahydrate, 0.01 wt% citric acid monohydrate, chitosan oligosaccharide lactate to γ-polyglutamic acid potassium salt mass ratio 1:0.50, composite pH 5.20, composite temperature 25℃, composite time 30 min, absolute pressure 0.09 MPa air atmosphere, 100 mesh filtration, spray drying inlet air temperature 120℃ and outlet air temperature 60℃.

[0074] Comparative Example 8: Basically the same as Example 1, except that γ-polyglutamic acid potassium salt was removed, and only chitosan oligosaccharide lactate was retained as the functional oligosaccharide component. The mass of chitosan oligosaccharide lactate was calculated as 0.20 wt% of the total mass of the ionic complex in Example 1. Other conditions were maintained as follows: urea 5.00 wt%, potassium dihydrogen phosphate 60.00 wt%, potassium nitrate 33.959 wt%, magnesium sulfate heptahydrate 0.20 wt%, zinc sulfate heptahydrate 0.05 wt%, ferrous sulfate heptahydrate 0.05 wt%, boric acid 0.02 wt%, manganese sulfate monohydrate 0.01 wt%, ammonium molybdate tetrahydrate 0.001 wt%, citric acid monohydrate 0.01 wt%, water 0.50 wt%, compound pH 5.20, temperature 25°C, stirring for 30 min, absolute pressure 0.09 MPa air atmosphere, 100 mesh filtration, spray drying inlet air temperature 120°C and outlet air temperature 60°C. This comparative example was used to investigate the synergistic relationship between chitosan oligosaccharide lactate and γ-polyglutamic acid potassium salt.

[0075] Comparative Example 9: Basically the same as Example 1, except that chitosan oligosaccharide lactate was removed, and only γ-polyglutamic acid potassium salt was retained as the polyanionic component. The mass of γ-polyglutamic acid potassium salt was calculated as 0.20 wt% of the total mass of the ionic complex in Example 1. Other conditions were maintained as follows: urea 5.00 wt%, potassium dihydrogen phosphate 60.00 wt%, potassium nitrate 33.959 wt%, magnesium sulfate heptahydrate 0.20 wt%, zinc sulfate heptahydrate 0.05 wt%, ferrous sulfate heptahydrate 0.05 wt%, boric acid 0.02 wt%, manganese sulfate monohydrate 0.01 wt%, ammonium molybdate tetrahydrate 0.001 wt%, citric acid monohydrate 0.01 wt%, water 0.50 wt%, composite pH 5.20, temperature 25°C, stirring for 30 min, absolute pressure 0.09 MPa air atmosphere, 100 mesh filtration, spray drying inlet air temperature 120°C and outlet air temperature 60°C. This comparative example was used to examine the synergistic relationship between chitosan oligosaccharide lactate and γ-polyglutamic acid potassium salt. Since this comparative example does not contain chitosan oligosaccharide lactate, the filtration retention rate of chitosan oligosaccharide lactate is not used as an evaluation item for this comparative example.

[0076] Comparative Example 10: Essentially the same as Example 1, except that the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ionic complex was not pre-formed. Instead, an aqueous solution of chitosan oligosaccharide lactate and an aqueous solution of γ-polyglutamic acid potassium salt were directly added to the fertilizer base mixture. The mass ratio of the two remained 1:0.50. Other conditions were maintained as follows: total functional components in the finished product: 0.20 wt%, urea: 5.00 wt%, potassium dihydrogen phosphate: 60.00 wt%, potassium nitrate: 33.959 wt%, magnesium sulfate heptahydrate: [The remaining text appears to be incomplete and requires further context.] The mixture consisted of 0.20 wt% zinc sulfate heptahydrate, 0.05 wt% ferrous sulfate heptahydrate, 0.05 wt% boric acid, 0.02 wt% manganese sulfate monohydrate, 0.01 wt% ammonium molybdate tetrahydrate, 0.01 wt% citric acid monohydrate, and 0.50 wt% water. The mixing conditions were: pH 5.20, temperature 25°C, stirring for 30 min, absolute pressure 0.09 MPa, air atmosphere, 100-mesh filtration, spray drying at an inlet air temperature of 120°C and an outlet air temperature of 60°C. This comparative example was used to investigate the effect of the pre-aqueous phase recombination step on the synergistic relationship.

[0077] Characterization and performance testing: Using 10wt% aqueous solutions prepared in Examples 1–4 and all comparative examples as test subjects, pH and water-insoluble matter were evaluated. The principle is that the acidity / alkalinity and undissolved residue after dissolution in the aqueous phase reflect the dispersion stability of water-soluble fertilizers. 10.00g of sample was added to 90.00g of deionized water, stirred at 25°C for 30min, and the pH and water-insoluble matter content were determined according to NY / T1973-2021 "Determination of Water-Insoluble Matter Content and pH of Water-Soluble Fertilizers". The average pH, standard deviation of pH, average water-insoluble matter content, and standard deviation of water-insoluble matter were recorded. A pH within the set range and a lower water-insoluble matter content indicate better water solubility and stability. NY / T1973-2021 is applicable to the determination of water-insoluble matter content and pH in liquid or solid water-soluble fertilizers.

[0078] Using the solid powders from Examples 1–4 and all comparative examples as test objects, the consistency of total nitrogen, phosphorus, and potassium content with the formulation was evaluated. The principle was to determine the consistency of macro-element input and finished product release by measuring nitrogen, phosphorus, and potassium after sample digestion or extraction. A testing procedure was established according to NY / T1977-2010 "Determination of Total Nitrogen, Phosphorus, and Potassium Content in Water-Soluble Fertilizers," with parallel measurements (n=3). The average value, standard deviation, average value, standard deviation, and average value of P2O5, K2O, and K2O standard deviation were recorded. A smaller deviation between the measured values ​​and the theoretical converted values ​​indicated better uniformity of the finished product. NY / T1977-2010 is applicable to the determination of total nitrogen, phosphorus, and potassium content in liquid or solid water-soluble fertilizers.

[0079] Using the solid powders from Examples 1–4 and all comparative examples as test objects, the content of magnesium, zinc, iron, boron, manganese, molybdenum, and calcium in calcium-containing samples was evaluated. The principle was to determine the retention and uniformity of micronutrients through water-soluble extraction, acidification, and spectroscopic or titration analysis. For zinc, iron, manganese, boron, and molybdenum, the method of NY / T1974-2010 was followed; for calcium and magnesium, the method of NY / T1117-2010 was followed. The average value, standard deviation, and relative deviation of each element were recorded. Smaller elemental deviations and the absence of abnormal precipitation indicated a more stable micronutrient addition process. Relevant standards were used for the determination of copper, iron, manganese, zinc, boron, molybdenum, calcium, magnesium, sulfur, and chlorine content in water-soluble fertilizers.

[0080] The retention rate of chitosan oligosaccharide lactate after 0.45 μm filtration was evaluated using an aqueous dispersion of the ion-exchange complex and a 10 wt% fertilizer aqueous solution. The principle is that the change in the mass of chitosan oligosaccharide lactate before and after filtration reflects the filtration stability of the complex. Filtration was performed at 25℃ using a 0.45 μm aqueous filter membrane. The chitosan oligosaccharide lactate content in the sample and filtrate before filtration was determined using high-performance anion exchange chromatography (HPLC). The retention rate was calculated using the retention rate formula, and the average and standard deviation were recorded. Higher values ​​indicate less filtration loss of functional components. No matching standard number was available for this experiment; specific detection steps and fields were recorded. For Comparative Example 9, since it did not contain chitosan oligosaccharide lactate, the retention rate was not calculated.

[0081] Using the aqueous dispersions of ion complexes from Examples 1–4 and Comparative Examples 8–10 as test subjects, hydrodynamic particle size, D90, polydispersity index, and Zeta potential were evaluated. The principle is that dynamic light scattering and electrophoretic light scattering reflect the size distribution and surface charge of the dispersion, respectively. The samples were diluted with deionized water to a complex mass fraction of 0.50 wt%, and tested at 25°C and pH 5.50–6.50. The average D90, standard deviation of D90, average polydispersity index, average Zeta potential, and standard deviation were recorded. A narrower distribution and a moderate potential are beneficial for evaluating the complex state.

[0082] Storage stability was evaluated using sealed samples from Examples 1–4 and all comparative examples. The principle was to reflect the hygroscopicity, precipitation, and functional component retention status of the powder by measuring changes in pH, water-insoluble matter, and chitosan oligosaccharide lactate retention rate after accelerated or room temperature storage. Samples were sealed and stored at 25°C and 40°C for 30, 90, and 180 days, respectively. A 10wt% aqueous solution was prepared and measured according to Experiments 1 and 4. The pH, water-insoluble matter, and retention rate were recorded after storage. Small pH drift, low water-insoluble matter, and high retention rate indicated good storage stability. The chitosan oligosaccharide lactate retention rate was not recorded for samples without chitosan oligosaccharide lactate.

[0083] Figure 1The graph shows the effect of the complex content on the retention rate of chitosan oligosaccharide lactate and water-insoluble matter. Based on the compounding process of Example 1, the mass ratio of chitosan oligosaccharide lactate to γ-polyglutamic acid potassium salt, the compounding pH, the stirring time, and the spray drying conditions were kept constant. Only the complex content was changed to 0.10 wt%, 0.20 wt%, 1.50 wt%, 2.60 wt%, 3.80 wt%, 5.00 wt%, and 6.00 wt%, and the changes in the retention rate of chitosan oligosaccharide lactate and water-insoluble matter in the finished product were investigated. The results show that when the complex content is too low, the retention rate is insufficient, and when the content is too high, the water-insoluble matter increases significantly. At a moderate content, a higher retention rate and a lower water-insoluble matter can be obtained, indicating that reasonable control of the complex addition amount is beneficial to balancing the retention of effective ingredients and water solubility stability.

[0084] Figure 2 The effect of the composite mass ratio on the retention rate of chitosan oligosaccharide lactate and the D90 of the composite was plotted. Using Example 1 as a baseline, the total composite content, composite pH, solid content, stirring time, and drying conditions were kept constant. Only the mass ratio of γ-polyglutamate potassium salt to chitosan oligosaccharide lactate was varied to 0.30, 0.50, 1.00, 2.00, 3.00, 4.00, and 4.50 times. The retention rate of chitosan oligosaccharide lactate and the D90 particle size of the composite were measured. The results showed that when the proportion of γ-polyglutamate potassium salt was too low, the composite protection was insufficient; when the proportion was too high, the particle size increased and the dispersibility decreased. A moderate mass ratio resulted in a smaller and more stable composite structure, indicating that this ratio range is beneficial for improving the retention of active components and the uniformity of the system.

[0085] Figure 3 The graph shows the effect of pH on the retention rate of chitosan oligosaccharide lactate and water-insoluble matter. Based on the raw material ratio, complex content, solid content, stirring conditions, and spray drying conditions of Example 1, only the pH during the compounding stage was changed to 5.00, 5.20, 5.60, 6.00, 6.40, 6.80, and 7.10 to investigate the retention rate of the effective components and the level of water-insoluble matter in the compounded product. The results show that both excessively low and excessively high pH are detrimental to stable compounding, resulting in a decrease in retention rate or an increase in water-insoluble matter. Higher retention rates and lower water-insoluble matter can be obtained in the weakly acidic to near-neutral range, indicating that the pH of the compound has a key influence on ion interactions and the solubility and stability of the finished product.

[0086] Figure 4The graph shows the effect of spray drying inlet air temperature on the retention rate of chitosan oligosaccharide lactate and the moisture content of the finished product. Based on the compound solution formulation, compound pH, compounding time, and feed solid content of Example 1, only the spray drying inlet air temperature was changed to 110℃, 120℃, 140℃, 150℃, 165℃, 180℃, and 190℃. The retention rate of chitosan oligosaccharide lactate and the moisture content of the finished product were then measured. The results show that when the temperature is too low, the moisture content of the finished product is too high, which is not conducive to storage stability; when the temperature is too high, the retention rate of the active ingredient decreases. A moderate inlet air temperature can achieve both low moisture content and high retention rate, indicating that the spray drying temperature needs to be controlled within a suitable range to ensure product quality.

[0087] Figure 5 The DLS differential particle size distribution diagrams for Examples 1, 8, and 10 are shown. Each sample was dispersed in water at the same concentration. After thorough hydration and equilibration, the hydrodynamic particle size distribution was determined using dynamic light scattering (DLS) to compare the particle dispersion under different composite conditions. The results show that the particle size distribution peak of Example 1 is narrower and mainly concentrated in the smaller particle size region, while the distribution peaks of Comparative Examples 8 and 10 shift towards larger particle sizes and exhibit a wider distribution. This indicates that the composite system formed in Example 1 has a more uniform dispersion and lower aggregation degree, demonstrating that its composite structure has better water dispersion stability.

[0088] Figure 6 The cumulative particle size distribution (DLS) curves for Examples 1, 8, and 10 are shown. Under the same sample concentration, dispersion medium, and detection conditions, the cumulative particle size distribution changes of each sample were statistically analyzed to compare differences in particle size parameters such as D90. The results show that the cumulative distribution curve of Example 1 is generally located in the smaller particle size range, and the particle size corresponding to 90% cumulative distribution is significantly lower than that of the comparative sample. The cumulative curves of Comparative Examples 8 and 10 shift to the right, indicating the presence of more large-size particles or aggregates in the system. This demonstrates that the composite process of Example 1 can effectively reduce the proportion of large particles and improve the uniformity of the system.

[0089] Figure 7 The Zeta potential distribution diagrams for Examples 1, 8, and 9 are shown. Each sample was prepared as an aqueous dispersion of the same concentration, and the Zeta potential distribution was measured under consistent ionic strength and testing temperature conditions to evaluate the surface charge state of the composite particles. The results show that the Zeta potential distribution of Example 1 is concentrated and within a relatively stable range, while Comparative Examples 8 and 9 exhibit potential shifts or wider distributions, indicating that improper formulation or pH conditions can lead to uneven surface charge. These results demonstrate a charge interaction between chitosan oligosaccharide lactate and γ-polyglutamic acid potassium salt in Example 1, and the composite state can be evaluated in conjunction with particle size and filtration retention rate.

[0090] Figure 8The diagram shows the paired chitosan oligosaccharide lactate content before and after filtration for Examples 1, 8, and 10. Each sample was prepared as an aqueous solution of the same concentration and filtered through a filter membrane of the same pore size. The chitosan oligosaccharide lactate content before and after filtration was measured, and the content loss during filtration was calculated. The results show that the content change before and after filtration was relatively small in Example 1, while the content decrease was more significant in Comparative Examples 8 and 10, indicating that the active ingredient in the comparative samples is more easily retained with insoluble particles or large aggregates. This result indicates that the composite system of Example 1 can improve the permeability and effective retention of chitosan oligosaccharide lactate in aqueous systems.

[0091] Figure 9 The scatter plots show the filtration retention rates of chitosan oligosaccharide lactate for Examples 1, 8, and 10. Parallel tests were performed on each sample under the same solution concentration, filter material, and detection method. The filtration retention rates are expressed as scatter plots and mean ± standard deviation. The results show that Example 1 has a higher mean filtration retention rate and smaller dispersion, while the retention rates of Comparative Examples 8 and 10 are significantly lower and fluctuate more. This indicates that Example 1 has better retention of active ingredients and intra-batch stability, demonstrating that the optimized composite conditions can reduce the loss of active ingredients during the filtration process.

[0092] Figure 10 The graphs show the changes in water-insoluble matter during storage for Examples 1, 5, and 6. Each sample was placed under the same packaging, temperature, humidity, and storage period. The water-insoluble matter content was measured at 0, 30, 90, and 180 days to evaluate long-term storage stability. The results show that in Example 1, the water-insoluble matter increased slowly and remained at a low level during storage, while the water-insoluble matter in Comparative Examples 5 and 6 increased significantly over time. This indicates that unreasonable combined conditions can easily lead to aggregation, precipitation, or decreased solubility during storage. These results demonstrate that Example 1 has better storage stability and water solubility retention.

[0093] Figure 11 The pH drift graphs for Examples 1, 5, and 6 during storage are shown. Samples were prepared as 10 wt% aqueous solutions at the same mass concentration. pH changes were measured at storage points of 0, 30, 90, and 180 days to evaluate the acid-base stability of the systems. The results showed that the pH of Example 1 changed little with storage time, remaining within a stable range overall. Comparative Examples 5 and 6, however, exhibited varying degrees of pH drift, with Comparative Example 6 showing a particularly high initial pH that persisted significantly after storage. These results indicate that the composite system of Example 1 can better buffer acid-base changes during storage, thus contributing to the maintenance of product physicochemical stability.

[0094] Figure 12The GPC / SEC molecular weight distribution maps of chitosan oligosaccharide lactate and γ-polyglutamic acid potassium salt are shown. Gel permeation chromatography or size exclusion chromatography were performed on the two core raw materials to compare their molecular weight distribution characteristics, providing basic parameters for the formation of the composite structure. The results show that chitosan oligosaccharide lactate is mainly distributed in the lower molecular weight range, while γ-polyglutamic acid potassium salt is distributed in the higher molecular weight range. The significant difference in molecular weight between the two is conducive to the formation of a composite system involving components of different molecular weights. These results indicate that the molecular weight characteristics of the raw materials are consistent with the design concept of constructing a stable composite structure in this scheme.

[0095] Figure 13 This study presents the first derivative plot of the potentiometric titration of γ-polyglutamic acid potassium salt to determine the degree of carboxyl potassium salt formation. Using γ-polyglutamic acid potassium salt samples as the test object, potentiometric titration was performed with potassium hydroxide standard solution. The titration jump point was determined by the first derivative curve to characterize the degree of carboxyl neutralization or potassium salt formation. The results show that the titration curve has a clear first derivative peak, indicating that the carboxyl reaction sites in the sample are well-defined, and the degree of potassium salt formation can be effectively determined by the titration endpoint. These results demonstrate that γ-polyglutamic acid potassium salt possesses a confirmed anionic carboxyl structure, providing anionic sites for ionic complexation or association with chitosan oligosaccharide lactate.

[0096] Figure 14 The image shows a macroscopic optical photograph comparison between the final product of Example 1 and the final product of Comparative Example 10, illustrating that the pre-formation of the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ionic complex is beneficial for obtaining a powdery functional water-soluble fertilizer with a more uniform appearance and less agglomeration. Figure 14 a is a macroscopic optical photograph of the final product of Example 1. The sample is a powdered functional water-soluble fertilizer obtained by spray drying. The finished product contains 0.20 wt% chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex, the pH of a 10 wt% aqueous solution is 5.50, the water-insoluble matter is 0.12 wt%, and the chitosan oligosaccharide lactate retention rate is 86.20%, showing that the pre-compounding, filtration, concentration and spray drying process can obtain a uniform powder with low water-insoluble matter. Figure 14 b is a macroscopic optical photograph of the final product of Comparative Example 10. The sample is a powdered functional water-soluble fertilizer obtained by directly adding two functional components without pre-forming the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex. It is used to compare the powder color, uniformity and agglomeration state with Example 1, showing that the pre-aqueous phase compounding step plays an important role in improving the uniformity of the final powder appearance and reducing local agglomeration.

[0097] Figure 15 The image shows a comparison of the SEM morphology of the final product of Example 1 and the final product of Comparative Example 10, illustrating that Example 1, by pre-forming a chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex, can improve the uniformity of particle distribution, particle profile, and surface microstructure of spray-dried powder. Figure 15 Image a is a low-magnification SEM image of the final product of Example 1, used to show the particle group and secondary agglomeration state of the spray-dried powder, showing that the powder of Example 1 has good particle dispersibility over a large area. Figure 15 b is a low-magnification SEM image of the final product of Comparative Example 10, used to show the distribution and agglomeration of powder particles under non-pre-composite conditions, showing that direct mixing of functional components is more likely to lead to local particle aggregation. Figure 15 c is a medium-magnification SEM image of the final product of Example 1, used to show the outline, equivalent particle size and particle adhesion state of single or small amounts of spray-dried powder particles, showing that the morphology of the powder particles in Example 1 is relatively complete. Figure 15 Image d is a medium-magnification SEM image of the final product of Comparative Example 10, used to show the particle outline, adhesion and irregular morphology in the uncomposite sample, showing that the precomposite process helps to reduce abnormal adhesion between particles. Figure 15 e is a high-magnification SEM image of the final product of Example 1, used to show the salt crystals, wrinkles, pores and rough structures on the surface of the powder particles, showing that the surface microstructure of Example 1 is relatively uniform. Figure 15 f is a high-magnification SEM image of the final product of Comparative Example 10, used to show the local roughness, salt crystal enrichment or microcrack features on the surface of the uncomposite sample, showing that the pre-formation of ionic complexes is beneficial to improving the distribution uniformity of organic functional components and inorganic salt system.

[0098] Figure 16 This is a macroscopic optical photographic evolution diagram of S1 to the final product in Example 1, used to show that this scheme achieves a stable transformation of functional water-soluble fertilizer from molecular solution to powder product through the continuous construction of γ-polyglutamic acid potassium salt aqueous solution, chitosan oligosaccharide lactate aqueous solution, ion complex aqueous dispersion, fertilizer mixture and final powder. Figure 16 Image a is a macroscopic optical photograph of an aqueous solution of S1γ-polyglutamic acid potassium salt, with a solid content of 1.00 wt%, pH of 6.50, and a carboxyl potassium salting degree of 70.00 mol%, showing that γ-polyglutamic acid can form a polyanionic aqueous phase system required for subsequent composites after potassium salting. Figure 16 b is a macroscopic optical photograph of an aqueous solution of S2 chitosan oligosaccharide lactate, with a concentration of 1.00 wt%, pH of 4.80, and a number-average molecular weight of 300 Da, indicating that chitosan oligosaccharide lactate can form an aqueous cationic component that is complexed with the polyanionic component. Figure 16 c is a macroscopic optical image of the aqueous dispersion of the S3 chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex. The composite pH was 5.20, the composite temperature was 25℃, the composite time was 30 min, and the D90 of the ion complex was 220 nm. This shows that a stable nanoscale composite dispersion can be obtained by controlling the pH and feed ratio. Figure 16Image d is a macroscopic optical photograph of fertilizer mixture S4. Urea, potassium dihydrogen phosphate, potassium nitrate and trace element salts were added to the system in sequence. The pH was controlled at 5.50 during the addition process, which shows that the pre-complex can maintain good compatibility in the high phosphorus and potassium fertilizer system. Figure 16 e is a macroscopic optical photograph of the S5 spray-dried powdered functional water-soluble fertilizer. The spray drying inlet air temperature was 120℃ and the outlet air temperature was 60℃. The resulting 10wt% aqueous solution had a pH of 5.50 and a water-insoluble content of 0.12wt%, indicating that this route can produce low water-insoluble powder products that meet the needs of drip irrigation, fertigation, and foliar spraying.

[0099] Table 1 Performance of Examples and Comparative Examples

[0100] As can be seen from the performance of the examples and comparative examples in the table, Examples 1–4 generally showed a relatively balanced trend in terms of water-insoluble matter, retention rate of chitosan oligosaccharide lactate after 0.45 μm filtration, complex D90, and water-insoluble matter after storage. In the conventional comparative examples, deviations in the complex pH, insufficient complexation time, changes in the order of adding ferrous sulfate heptahydrate, or increased moisture content of the finished product all caused adverse changes in water-insoluble matter, D90, or water-insoluble matter after storage. In the synergistic comparative examples, the retention rate and dispersion state decreased to varying degrees after the absence of chitosan oligosaccharide lactate, the absence of γ-polyglutamic acid potassium salt, or the cancellation of pre-aqueous phase complexation. This indicates that the data trend corresponds to the natural contradiction between the effective retention and dispersion stability of functional components.

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A functional water-soluble fertilizer containing chitosan oligosaccharide lactate, characterized in that, Based on a total mass of 100 wt% of the finished functional water-soluble fertilizer product, it includes the following components converted from the corresponding feed ingredients: The chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ionic complex is 0.20-5.00 wt%, wherein the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ionic complex is formed by the electrostatic interaction between chitosan oligosaccharide lactate and γ-polyglutamic acid potassium salt, wherein the γ-polyglutamic acid potassium salt is formed by the neutralization of γ-polyglutamic acid with potassium hydroxide; Urea 5.00-40.00 wt%; Potassium dihydrogen phosphate 10.00-60.00 wt%; Potassium nitrate 5.00-50.00 wt%; Magnesium sulfate heptahydrate 0.20-8.00 wt%; Zinc sulfate heptahydrate 0.05-3.00 wt%; Ferrous sulfate heptahydrate 0.05-3.00 wt%; Boric acid 0.02-3.00 wt%; Manganese sulfate monohydrate 0.01-1.00 wt%; Ammonium molybdate tetrahydrate 0.001-0.20 wt%; Optional calcium nitrate tetrahydrate 0.10-3.00 wt%, when containing the calcium nitrate tetrahydrate, the mass ratio of the calcium nitrate tetrahydrate to the potassium dihydrogen phosphate is 0.02-0.30:1; Citric acid monohydrate 0.01-1.50 wt%; Moisture 0.50-5.00wt%; The mass ratio of chitosan oligosaccharide lactate to γ-polyglutamic acid potassium salt in the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex is 1:0.50-4.00; the pH value of the functional water-soluble fertilizer when formulated into a 10wt% aqueous solution is 5.50-6.80, the water-insoluble matter is 0.05-0.80wt%, and the chitosan oligosaccharide lactate retention rate after 0.45μm filtration is 80.00-99.00%; the content of the above components is selected within the range that makes the sum of the contents of all components in the functional water-soluble fertilizer 100wt%, wherein the content of potassium nitrate is adjusted according to the content of other components within the range.

2. The functional water-soluble fertilizer according to claim 1, characterized in that, The chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex was prepared by the following steps: A1. Provides an aqueous solution of chitosan oligosaccharide lactate and an aqueous solution of potassium γ-polyglutamate, wherein the aqueous solution of chitosan oligosaccharide lactate contains 1.00-15.00 wt% chitosan oligosaccharide lactate, and the aqueous solution of potassium γ-polyglutamate contains 1.00-30.00 wt% potassium γ-polyglutamate. A2. The aqueous solution of chitosan oligosaccharide lactate and the aqueous solution of γ-polyglutamic acid potassium salt are mixed at a mass ratio of chitosan oligosaccharide lactate to γ-polyglutamic acid potassium salt of 1:0.50-4.00, and stirred at 25-45℃ for 30-120 min at pH 5.20-6.80 to obtain the composite mixture. A3. Filter the composite mixture to obtain the aqueous dispersion of the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex.

3. The functional water-soluble fertilizer according to claim 2, characterized in that, In step A2, the composite is carried out under an absolute pressure of 0.09-0.11 MPa and an air atmosphere. The composite process ends when the pH change of the mixed system after composite does not exceed 0.20 within 30 minutes and no flocculent matter is retained after filtration through a 100 μm sieve. The filtration in step A3 is carried out using a 100-200 mesh sieve. The aqueous dispersion of the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex obtained in step A3 is dried at 45-75℃ for 2-8 hours to obtain a solid chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex. The quality control parameters of the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex are: water-insoluble matter of 0.05-0.80 wt% and chitosan oligosaccharide lactate retention rate of 80.00-99.00% after 0.45 μm filtration.

4. The functional water-soluble fertilizer according to claim 2, characterized in that, The aqueous solution of potassium γ-polyglutamic acid in step A1 is prepared by the following steps: B1. Add 100 parts by weight of γ-polyglutamic acid to 300-3000 parts by weight of deionized water and stir at 20-40℃ for 0.5-2.0h to obtain γ-polyglutamic acid hydrated solution; B2. Add a 5.00-30.00 wt% potassium hydroxide aqueous solution to the γ-polyglutamic acid hydrate solution, controlling the temperature at 20-40℃ and the pH at 6.50-8.00 during the addition process, and continue stirring for 0.5-2.0 h to obtain a γ-polyglutamic acid potassium salt aqueous solution. B3. The neutralization adjustment is terminated when the pH change of the γ-polyglutamic acid potassium salt aqueous solution does not exceed 0.20 within 30 minutes; B4. The γ-polyglutamic acid potassium salt aqueous solution is filtered through a 100-200 mesh filter and then adjusted by adding water or concentration to obtain a γ-polyglutamic acid potassium salt aqueous solution with a solid content of 1.00-30.00 wt% and a carboxyl potassium salt concentration of 70.00-100.00 mol%.

5. The functional water-soluble fertilizer according to claim 2, characterized in that, The chitosan oligosaccharide lactate aqueous solution in step A1 is prepared by the following steps: C1. Add 100 parts by weight of chitosan oligosaccharide lactate to 600-10000 parts by weight of deionized water, wherein the number average molecular weight of chitosan oligosaccharide lactate is 300-5000 Da; C2. Stir at 20-40℃ and 0.09-0.11MPa absolute pressure for 20-60 min to obtain a crude solution of chitosan oligosaccharide lactate; C3. The pH of the crude chitosan oligosaccharide lactate solution was adjusted to 4.80-6.50 using citric acid monohydrate and a potassium hydroxide aqueous solution with a mass concentration of 5.00-30.00 wt%. C4. The crude chitosan oligosaccharide lactate solution after pH adjustment is filtered through a 100-200 mesh filter, and after water replenishment or concentration adjustment, an aqueous solution of chitosan oligosaccharide lactate is obtained, wherein the water-insoluble matter in the aqueous solution of chitosan oligosaccharide lactate is not higher than 1.00 wt%.

6. The functional water-soluble fertilizer according to claim 2, characterized in that, The magnesium sulfate heptahydrate, zinc sulfate heptahydrate, ferrous sulfate heptahydrate, boric acid, manganese sulfate monohydrate, and ammonium molybdate tetrahydrate are added through the following steps: D1. Prepare aqueous solutions of magnesium sulfate heptahydrate, zinc sulfate heptahydrate, ferrous sulfate heptahydrate, boric acid, manganese sulfate monohydrate and ammonium molybdate tetrahydrate with a mass concentration of 1.00-30.00 wt% respectively. D2. Mix the aqueous dispersion of chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex obtained in step A3 with urea, potassium dihydrogen phosphate and potassium nitrate, and then add the aqueous solutions obtained in step D1 in batches at 25-45℃. The addition time for each batch is 5-30 min, and the total addition time is 30-120 min. D3. During the addition process, control the pH to 5.50-6.80; D4. After the addition is complete, continue stirring for 20-60 minutes until the resulting mixture has no visible precipitate and the water-insoluble matter is no more than 0.80 wt%.

7. A method for preparing a functional water-soluble fertilizer containing chitosan oligosaccharide lactate as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Provides a pre-prepared aqueous dispersion of a chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ionic complex obtained by mixing and filtering chitosan oligosaccharide lactate aqueous solution and γ-polyglutamic acid potassium salt aqueous solution at a mass ratio of chitosan oligosaccharide lactate to γ-polyglutamic acid potassium salt of 1:0.50-4.00 at pH 5.20-6.80; S2. Add urea, potassium dihydrogen phosphate, potassium nitrate, magnesium sulfate heptahydrate, zinc sulfate heptahydrate, ferrous sulfate heptahydrate, boric acid, manganese sulfate monohydrate and ammonium molybdate tetrahydrate, and optionally calcium nitrate tetrahydrate to the aqueous dispersion of the chitosan oligosaccharide lactate-γ-polyglutamic acid potassium salt ion complex to obtain a liquid mixture. S3. Using citric acid monohydrate and a potassium hydroxide aqueous solution with a mass concentration of 5.00-30.00wt%, the pH of the liquid mixture is adjusted to 5.50-6.80, followed by filtration, concentration and drying to obtain the functional water-soluble fertilizer.

8. The preparation method according to claim 7, characterized in that, In step S2, urea, potassium dihydrogen phosphate, and potassium nitrate are added first, followed by magnesium sulfate heptahydrate, zinc sulfate heptahydrate, ferrous sulfate heptahydrate, boric acid, manganese sulfate monohydrate, and ammonium molybdate tetrahydrate. During the addition process, the temperature is controlled at 25-45℃ and the pH at 5.50-6.

80. The ferrous sulfate heptahydrate is added after the zinc sulfate heptahydrate, boric acid, manganese sulfate monohydrate, ammonium molybdate tetrahydrate, and calcium nitrate tetrahydrate (if present). After adding the ferrous sulfate heptahydrate, stirring is continued for 20-60 minutes.

9. The preparation method according to claim 7, characterized in that, In step S3, the filtration is carried out using a 100-200 mesh filter. After filtration, the solution is concentrated to obtain a solid content of 30.00-70.00 wt%. The concentrated solution is then spray-dried at an inlet air temperature of 120-180℃ and an outlet air temperature of 60-90℃ to obtain a solid functional water-soluble fertilizer with a moisture content of 0.50-5.00 wt%.

10. The preparation method according to claim 7, characterized in that, Steps S1 to S3 are completed using an intermittent or continuous aqueous phase process. No organic solvents are used in steps S1 to S3. The pH of the material system in steps S1 to S3 is controlled online at 5.20-6.

80. When the functional water-soluble fertilizer obtained after step S3 is formulated into an aqueous solution with a mass fraction of 10wt%, the pH value is 5.50-6.80 and the water-insoluble matter is 0.05-0.80wt%.

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