Water-soluble fertilizer for stress resistance and yield increase of winter wheat and preparation method of water-soluble fertilizer

Abstract

The invention belongs to the field of agricultural fertilizers, and provides a stress-resistant and yield-increasing water-soluble fertilizer for winter wheat and a preparation method of the stress-resistant and yield-increasing water-soluble fertilizer. A core-shell nano composite intermediate A and free fulvic acid are synergistically designed, ammonium polyphosphate and poly-gamma-glutamic acid form a prepolymer core, fulvic acid coats the prepolymer core, and zinc and iron salts are complexed on the surface in situ to form a nano shell layer, so that large nutrients and trace elements are integrated in a stable dispersion system; the low-viscosity pumpable characteristic that the full-temperature-zone viscosity is not higher than 300 mPa.s under the high nutrient formula condition of 15-22 wt% of total nitrogen, 5-12 wt% of total phosphorus and 8-18 wt% of total potassium is achieved, the clarification stability that no crystal is separated out after standing for 7 days at the temperature of-5 DEG C and the PDI is not larger than 0.25 is achieved, and the synergistic interaction of slow release and effective form maintenance of zinc and iron elements in the form of core-shell nanoparticles is achieved; the technical contradictions that a high-nutrient water-soluble fertilizer is poor in processing adaptability and easy to crystallize and layer at low temperature and microelements are easy to hydrolyze and inactivate are solved, and the high-nutrient water-soluble fertilizer has wide winter wheat topdressing application value.

Description

Technical Field

[0001] This invention relates to the field of agricultural fertilizers, specifically to a water-soluble fertilizer for winter wheat that promotes stress resistance and yield increase, and its preparation method. Background Technology

[0002] Winter wheat, an important food crop in my country, is widely planted in the North China Plain, the Huang-Huai-Hai Plain, and the Northwest winter wheat region. Its yield and quality are directly related to national food security. During the winter wheat growth cycle, the greening and jointing stages and the grain-filling stages are critical periods for nutrient demand and crucial stages that determine yield and quality. Under modern intensive farming models, winter wheat faces multiple adverse pressures such as low-temperature freezing damage, drought stress, soil salinization, and pests and diseases, placing higher demands on fertilizers for efficient nutrient utilization, stress resistance and yield-increasing functions, and ease of application. High-nutrient water-soluble fertilizers, due to their high nutrient content, good water solubility, rapid absorption, and ability to be integrated with irrigation systems for precise fertilization, are increasingly widely used in topdressing winter wheat. High-nutrient water-soluble fertilizers need to simultaneously meet the needs for sufficient supply of macronutrients (nitrogen, phosphorus, and potassium), synergistic supplementation of micronutrients (zinc, iron, and magnesium), and the promoting effects of organic active substances such as humic acid and amino acids on root growth and stress resistance. Especially when applied under low-temperature conditions, the fertilizer's solubility, stability, and the availability of trace elements become key factors restricting its performance. Therefore, developing a water-soluble fertilizer specifically for winter wheat that combines high nutrient content, low-temperature clarification and stability, slow-release and synergistic effects of trace elements, and excellent processing performance is of great significance for improving winter wheat yield and stress resistance, and promoting the advancement of fertigation technology.

[0003] Currently, commercially available high-nutrient water-soluble fertilizers still face several technological bottlenecks. On the one hand, to achieve high nutrient content (such as total nitrogen, phosphorus, and potassium exceeding 35%) and low cost, the formulations often use highly soluble inorganic salts such as urea, ammonium nitrate, ammonium polyphosphate, and potassium nitrate as the main nutrient sources. However, the combination of high ionic strength and high solid content leads to a sharp increase in system viscosity, reaching 500-1200 mPa·s at room temperature. This makes continuous mixing and filling difficult using conventional pumping systems, severely restricting production efficiency and equipment adaptability. On the other hand, high-concentration multi-component salt solutions are prone to instability phenomena such as crystallization and stratification during low-temperature storage or temperature fluctuations. For example, Chinese patent CN112624849A discloses a method for preparing a high-solubility nitrogen and phosphorus water-soluble fertilizer, but salt crystallization easily occurs below zero degrees Celsius, seriously affecting product appearance and application uniformity. Furthermore, trace elements such as zinc and iron are prone to hydrolysis and precipitation or the formation of macromolecular complexes in complex systems containing polyphosphates and organic ligands, thus losing their effectiveness. For example, Chinese patent CN107827580A discloses a water-soluble fertilizer containing humic acid and its preparation method. However, due to the strong complexing effect of phosphate, zinc and iron salts rapidly hydrolyze within the pH range of 5-7 to form insoluble phosphate precipitates, resulting in a decrease in trace element effectiveness of more than 40%. The root cause of the above problems lies in the fact that the strong electrostatic attraction between ions and the hydrogen bond network under high nutrient formulation conditions lead to a sharp contradiction between the fluidity and stability of the system. Trace elements are difficult to simultaneously achieve stable immobilization, slow-release control, and effective form retention in environments with strong oxidizing and complexing properties. Existing technologies lack effective means to solve this coupling contradiction from the perspective of nanostructure design. Summary of the Invention

[0004] The purpose of this invention is to provide a water-soluble fertilizer for winter wheat to resist stress and increase yield, and its preparation method. This invention addresses the technical contradictions of current high-nutrient water-soluble fertilizers, which are difficult to balance low viscosity, continuous pumping and mixing, and filterable filling under high ionic strength and high solid content formulation conditions; are prone to crystallization and stratification during storage and temperature cycling at -5℃ to 40℃, resulting in insufficient clarification stability; and are prone to hydrolysis or complexation and inactivation of trace elements such as zinc and iron in polyphosphate and organic ligand systems, as these elements are difficult to achieve stable immobilization and slow release while maintaining their effective form.

[0005] This invention employs a synergistic approach combining a core-shell nanocomposite intermediate A with free fulvic acid. A prepolymer P, formed in an aqueous phase by ammonium polyphosphate and polyγ-glutamic acid, possesses steric hindrance and electrostatic stability properties, serving as the nanocore. Fulvic acid, through its carboxyl and hydroxyl groups, forms a hydrogen bond network with the phosphate and amino groups in the prepolymer, coating the core surface. Zinc-iron salts, under the complexation of fulvic acid ligands and pH control, are deposited in situ to form a nanoshell of controllable thickness, achieving the transformation of trace elements from a free state to a nano-supported state. Simultaneously, free fulvic acid, through hydrogen bonding with the nanoparticle surface and weak complexation with inorganic salts in the solution phase, constructs a ternary synergistic stable network of "nanoparticle-organic ligand-inorganic salt." This significantly reduces system viscosity and inhibits low-temperature crystallization while ensuring high macro-element content, and endows trace elements with the dual functions of slow release and effective form preservation, thus achieving synergistic effects.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A water-soluble fertilizer for stress resistance and yield enhancement in winter wheat, wherein the water-soluble fertilizer is an aqueous solution using deionized water as a solvent, comprising the following components, based on the total mass of the finished product:

[0008] (1) The total nitrogen is 15–22 wt%, which is provided by urea, ammonium nitrate, and ammonium polyphosphate, and optionally also includes potassium nitrate to provide nitrate nitrogen, and the mass ratio of ammonium nitrogen to nitrate nitrogen is 20:80 to 80:20, wherein the mass ratio of ammonium nitrogen to nitrate nitrogen is calculated based on the nitrogen provided by nitrogen-containing salts other than urea;

[0009] (2) The total phosphorus nutrient content, converted to phosphorus pentoxide, is 5–12 wt%, which is provided by ammonium polyphosphate;

[0010] (3) The total potassium nutrient content, converted to potassium oxide, is 8–18 wt%, provided by at least one of potassium nitrate and potassium sulfate;

[0011] (4) 0.5–5.0 wt% of solids containing core-shell nanocomposite intermediate A, wherein core-shell nanocomposite intermediate A is formed by the reaction of ammonium polyphosphate, polyγ-glutamic acid, fulvic acid, zinc sulfate heptahydrate and ferrous sulfate heptahydrate in an aqueous phase;

[0012] (5) Contains 0.1–1.0 wt% free fulvic acid, wherein the free fulvic acid is fulvic acid added in addition to the fulvic acid contained in the core-shell nanocomposite intermediate A;

[0013] (6) Contains magnesium sulfate heptahydrate, with a medium element nutrient content of 0.5–3.0 wt% when converted to magnesium oxide;

[0014] (7) Contains 0.1–0.8 wt% of trisodium citrate dihydrate, wherein the trisodium citrate dihydrate is used as a complexing agent;

[0015] (8) The total zinc content in the finished product is 0.02–0.20 wt%, and the total iron content is 0.02–0.20 wt%, wherein zinc and iron are at least partially present in the shell form of the core-shell nanocomposite intermediate A, and optionally also in the free form of at least one of zinc sulfate heptahydrate and ferrous sulfate heptahydrate;

[0016] (9) The remainder is deionized water and unavoidable impurities.

[0017] Furthermore, the total nitrogen is provided by urea, ammonium nitrate, ammonium polyphosphate, and potassium nitrate, and the finished product may optionally also include potassium nitrate to provide nitrate nitrogen. The nitrogen provided by urea accounts for 20–60 wt% of the total nitrogen, and the mass ratio of ammonium nitrogen to nitrate nitrogen is calculated based on the nitrogen provided by nitrogen-containing salts other than urea. Ammonium nitrogen includes ammonium nitrogen provided by ammonium nitrate and ammonium polyphosphate, and nitrate nitrogen includes nitrate nitrogen provided by ammonium nitrate and, if present, potassium nitrate. The nitrogen provided by urea is not included in the calculation of the mass ratio of ammonium nitrogen to nitrate nitrogen.

[0018] Furthermore, in the water-soluble fertilizer for stress resistance and yield increase of winter wheat, the core of the core-shell nanocomposite intermediate A is a prepolymer P. The prepolymer P is a prepolymer formed by ammonium polyphosphate and polyγ-glutamic acid, and the prepolymer P is prepared by a method including the following steps:

[0019] A1. Dissolve 100–150 parts by mass of ammonium polyphosphate in deionized water at 50–70℃ to obtain a homogeneous solution. Slowly add 3–20 parts by mass of polyγ-glutamic acid at 60–80℃ with continuous stirring to make the mass ratio of ammonium polyphosphate to polyγ-glutamic acid 100:3–20. Continue stirring for 1–3 hours.

[0020] A2. Use a sodium hydroxide solution with a mass fraction of 10-40 wt% or a hydrochloric acid solution with a mass fraction of 10-37 wt%, add it dropwise under stirring and monitor it in real time with a pH meter, adjust the pH value of the reaction solution to 5.5-6.5, and add the amount to achieve the target pH.

[0021] A3. Concentrate the reaction solution under reduced pressure at 50–70°C to a solids mass fraction of 30–45 wt%.

[0022] A4. When the viscosity of the prepolymer solution at 25°C is 500–3000 mPa·s, and the pH value changes by no more than 0.2 within 30 minutes under constant temperature conditions at 25°C, the concentration is stopped, the solution is cooled, and insoluble matter is removed through a 100-mesh filter to obtain the prepolymer P.

[0023] Furthermore, the preparation of the core-shell nanocomposite intermediate A includes the following steps:

[0024] B1. Take 100 parts by weight of prepolymer P, based on the solids of prepolymer P, dilute with deionized water to a solids mass fraction of 10-25 wt%, and mechanically stir at 200-600 rpm for 10-30 min at 35-45℃.

[0025] B2. Based on the solids of prepolymer P, add 5–40 parts by mass of fulvic acid to the solution obtained in step B1 based on 100 parts by mass of prepolymer P, and stir at 35–45°C for 0.5–1.5 h.

[0026] B3. Preparation of metal salt solution: Dissolve zinc sulfate heptahydrate and ferrous sulfate heptahydrate in deionized water, controlling the molar ratio of zinc to iron to be 0.5–3:1, to prepare a mixed metal salt solution with a zinc ion concentration of 0.5–10 g / L and an iron ion concentration of 0.5–10 g / L; the volume of the metal salt solution is 5–20% of the total volume of the system obtained in step B2. The metal salt solution is added dropwise to the system in step B2 at a rate of 0.5-5 mL / min at 35-55°C, while trisodium citrate dihydrate is added simultaneously, so that the molar ratio of trisodium citrate dihydrate to the total amount of zinc and iron is 0.1-0.5:1. A sodium hydroxide solution with a mass fraction of 10-40 wt% or a hydrochloric acid solution with a mass fraction of 10-37 wt% is used. The solution is added dropwise under stirring and monitored in real time with a pH meter. The pH value is adjusted to 5.0-6.5, and the amount added is based on achieving the target pH. Stirring is continued for 1-3 hours.

[0027] B4. After step B3, apply high shear dispersion at 3000–6000 rpm to the reaction solution for 10–30 min, and then perform ultrasonic treatment at a frequency of 20–40 kHz and a sound power density of 0.5–1.5 W / cm² for 5–15 min.

[0028] B5. Large particles or gels are removed by filtration through a filter cartridge with a pore size of 1–5 μm to obtain a dispersion of core-shell nanocomposite intermediate A, wherein the nanoparticles in the dispersion have a D 50 The nanoparticles have a size of 50–150 nm, a PDI of no more than 0.25, and contain 5–15 wt% zinc and iron in their shells on a dry basis. The pH value is 5.0–6.5, and no visible precipitation is observed after standing for 24 hours.

[0029] Furthermore, the viscosity of the water-soluble fertilizer was measured using a rotational viscometer. The viscosity measured at any temperature within the temperature range of −5℃ to 40℃ was not higher than 300 mPa·s. After standing at −5℃ for 7 days, there was no crystallization or obvious stratification. Moreover, the conductivity of the solution prepared at 25℃ with a mass fraction of 10wt% was 15–40 mS / cm.

[0030] The viscosity at 25°C is not higher than 150 mPa·s;

[0031] No visible crystallization occurred when the mixture was left to stand in a sealed container at 0°C for 7 days.

[0032] The content of water-insoluble matter is not higher than 0.2 wt%;

[0033] The pH value is 5.5–7.0.

[0034] As a concept of this invention, the core-shell nanocomposite intermediate A is synergistically designed with free fulvic acid to enhance the low viscosity pumpability, low-temperature clarification stability, and slow-release synergistic effect of high-nutrient water-soluble fertilizers. Ammonium polyphosphate and polyγ-glutamic acid form a prepolymer P in the aqueous phase through electrostatic attraction and hydrogen bonding between phosphate groups and amino and carboxyl groups. The long-chain structure of polyγ-glutamic acid forms a protective layer with steric hindrance on the surface of the prepolymer, effectively inhibiting the aggregation between prepolymer particles. Simultaneously, the incompletely neutralized phosphate groups in the prepolymer impart a negative charge to the particle surface, further improving dispersion stability through electrostatic repulsion. Fulvic acid, as a natural organic ligand, coats the surface of the prepolymer core. Its multi-carboxyl and multi-hydroxyl structures form a dense hydrogen bond network with the phosphate and amino groups in the prepolymer. Under the complexation effect of the fulvic acid ligand and pH control, zinc-iron salts are deposited in situ within the fulvic acid coating layer, forming a nanoshell. This achieves the transformation of trace elements from a free state to a nano-supported state. The shell thickness is precisely controlled by adjusting the amount of fulvic acid and the acceleration rate of the metal salt droplets. The introduction of core-shell nanoparticles reduces the system viscosity through the following mechanisms: the high specific surface area and negative surface charge of the nanoparticles form an electric double layer structure with the inorganic cations in the solution phase, weakening the electrostatic attraction between free ions; the fulvic acid ligands form weak hydrogen bonds with small molecules such as urea and ammonium nitrate, disrupting the hydrogen bond network formed under high concentration conditions, thereby reducing the system viscosity. Free fulvic acid constructs a ternary synergistic stable network of nanoparticles, organic ligands, and inorganic salts through hydrogen bonding with the surface of nanoparticles and weak complexation with inorganic salts in the solution phase. This network inhibits the nucleation and growth of inorganic salt crystals under low-temperature conditions, while also endowing trace elements with the dual functions of slow release and preservation of effective forms. Compared with single macro-element formulations or conventional trace element addition methods, it exhibits significant synergistic effects.

[0035] This invention also discloses a method for preparing the above-mentioned water-soluble fertilizer for stress resistance and yield increase in winter wheat, the method comprising the following steps:

[0036] S1. Add deionized water to the reaction vessel, wherein the amount of deionized water added is 10-30 wt% of the total mass of the finished product. At 30-60°C, add at least one of ammonium polyphosphate, urea, ammonium nitrate, potassium nitrate and potassium sulfate, as well as magnesium sulfate heptahydrate, in sequence. Stir for 30-60 min until completely dissolved, and the solution is clear to the naked eye and free of visible solid particles as the criterion.

[0037] S2. When the reaction solution temperature is 25–45℃, add a dispersion of core-shell nanocomposite intermediate A, wherein the solid mass fraction of the dispersion of core-shell nanocomposite intermediate A is 5–25 wt%, and the amount of the dispersion of core-shell nanocomposite intermediate A added is 2–40 wt% of the total mass of the finished product, so that the solid mass fraction of the core-shell nanocomposite intermediate A in the finished product is 0.5–5.0 wt%, and maintain a shear speed of 1000–3000 rpm for stirring for 10–30 min;

[0038] S3. Under conditions of 20–40℃, add free fulvic acid (0.1–1.0 wt% of the total mass of the finished product) and trisodium citrate dihydrate (0.1–0.8 wt% of the total mass of the finished product), continue stirring for 20–40 min, and add the solution dropwise using a sodium hydroxide solution with a mass fraction of 10–40 wt% or a hydrochloric acid solution with a mass fraction of 10–37 wt% under stirring conditions, and monitor the pH value in real time with a pH meter, and adjust the pH value to 5.5–7.0, with the amount added based on achieving the target pH.

[0039] S4. Cool the mixed solution obtained in step S3 to no higher than 30°C, filter it through a filter element with a pore size of 5–20 μm to remove water-insoluble matter, and fill and seal it under the condition that the water-insoluble matter content is no higher than 0.2 wt% to obtain the winter wheat stress-resistant and yield-increasing water-soluble fertilizer.

[0040] Furthermore, in step S1, the order of feeding at least one of ammonium polyphosphate, urea, ammonium nitrate, potassium nitrate and potassium sulfate, and magnesium sulfate heptahydrate is ammonium polyphosphate, urea, ammonium nitrate, potassium nitrate and potassium sulfate, and magnesium sulfate heptahydrate.

[0041] Furthermore, in step S2, the shearing and stirring speed is 1500–2500 rpm, the shearing time is 15–25 min, and an ultrasonic field is applied during the shearing and stirring process. The frequency of the ultrasonic field is 20–40 kHz, the sound power density is 0.5–1.5 W / cm², and the ultrasonic time is 5–15 min.

[0042] Furthermore, in step S3, the amount of free fulvic acid added is controlled so that the mass fraction of fulvic acid in the finished product is 0.2–0.8 wt%, and the amount of trisodium citrate dihydrate added is controlled so that the mass fraction of trisodium citrate dihydrate in the finished product is 0.1–0.5 wt%.

[0043] Furthermore, in step S4, the solution is subjected to cooling aging at 0–5℃ for 2–24 hours before filtration to remove potential crystal nuclei, thereby improving the low-temperature storage stability of the finished product. The preparation method is a continuous production process. Steps S1–S4 are connected by an online metering pump, a static mixer, and an online pH and conductivity detection unit. The batch-to-batch deviation of the mass fractions of total nitrogen, total phosphorus, and total potassium in each batch of finished product is controlled to be no more than ±5%. The water-soluble fertilizer for winter wheat stress resistance and yield increase obtained by the preparation method is subjected to temperature cycling treatment of −5–40℃. One cycle consists of holding at −5℃ for 24 hours and holding at 40℃ for 24 hours. After a total of 3 cycles, the water-insoluble matter content increases by no more than 0.1 mass fraction points.

[0044] Furthermore, the total nitrogen is provided by urea, ammonium nitrate, ammonium polyphosphate and potassium nitrate, and the finished product may optionally also include potassium nitrate to provide nitrate nitrogen, and the nitrogen provided by urea accounts for 20-60 wt% of the total nitrogen.

[0045] Furthermore, the mass ratio of ammonium nitrogen to nitrate nitrogen is calculated based on the nitrogen provided by nitrogen-containing salts other than urea. Ammonium nitrogen includes ammonium nitrogen provided by ammonium nitrate and ammonium polyphosphate, and nitrate nitrogen includes nitrate nitrogen provided by ammonium nitrate and, if present, potassium nitrate. Nitrogen provided by urea is not included in the calculation of the mass ratio of ammonium nitrogen to nitrate nitrogen.

[0046] Furthermore, the proportion of nitrogen provided by potassium nitrate in the total nitrogen is 0–30 wt%.

[0047] Furthermore, in the core-shell nanocomposite intermediate A, zinc and iron exist in the form of shells, accounting for 30–100 wt% of the total zinc element and 30–100 wt% of the total iron element.

[0048] Furthermore, the absolute value of the zeta potential of the core-shell nanocomposite intermediate A dispersion at 25°C is not less than 20mV.

[0049] Furthermore, the solid mass fraction of the dispersion of the core-shell nanocomposite intermediate A is 5–25 wt%.

[0050] Furthermore, in step A1, the amount of deionized water added is such that the ammonium polyphosphate forms a solution with a mass fraction of 15–40 wt% after dissolution.

[0051] Furthermore, in step A1, the slow addition of polyγ-glutamic acid is done in batches or continuously over 30–120 minutes.

[0052] Furthermore, in step A2, the pH of the reaction solution is adjusted to 5.5–6.5 using a sodium hydroxide solution with a mass fraction of 10–40 wt% or a hydrochloric acid solution with a mass fraction of 10–37 wt%.

[0053] Furthermore, in step A3, the pressure reduction condition is an absolute pressure of 1–20 kPa inside the vessel.

[0054] Furthermore, in step B3, the zinc ion concentration in the metal salt solution is 0.5–10 g / L, and the iron ion concentration is 0.5–10 g / L.

[0055] Furthermore, in step B3, the dripping is completed within 30–120 minutes.

[0056] Furthermore, in step B5, the D 50 PDI was measured using dynamic light scattering at a temperature of 25°C.

[0057] Furthermore, the viscosity of the water-soluble fertilizer was measured using a rotational viscometer at 25°C.

[0058] As another aspect of this invention, the stepwise dissolution-nanoparticle dispersion-organic ligand synergistic stabilization preparation process is mainly used to enhance the processing controllability, component dispersion uniformity, and batch stability of the finished product. Step S1 employs a temperature-controlled dissolution and sequential feeding strategy. The preferential dissolution of ammonium polyphosphate can avoid side reactions or the formation of unstable complex salts with components such as urea and ammonium nitrate under high concentration conditions. Urea, as a hydrogen bond donor, forms a hydrogen bond network with the ammonium polyphosphate solution at 30-60℃, which is beneficial to the rapid dissolution of subsequent components. The addition of potassium nitrate and potassium sulfate is arranged after urea to utilize the solubilizing effect of urea on potassium salts. The magnesium sulfate heptahydrate is added last to avoid premature complexation with phosphate ions to form insoluble magnesium salts in a high nitrogen and high phosphorus environment. Step S2 involves adding the core-shell nanocomposite intermediate A dispersion within a moderate temperature range of 25-45℃. This ensures the thermal stability of the nanoparticles and utilizes the temperature-dependent viscosity regulation to promote uniform dispersion of the nanoparticles in a high ionic strength solution. Shear stirring at 1000-3000 rpm and ultrasonic-assisted treatment effectively break up the soft agglomeration of the nanoparticles, allowing D... 50The concentration is maintained within the 50-150 nm range. In step S3, free fulvic acid and trisodium citrate dihydrate are added at a relatively low temperature of 20-40℃. This prevents fulvic acid from undergoing oxidative degradation or irreversible complexation with inorganic salts at high temperatures. Trisodium citrate dihydrate acts as a weak complexing agent, forming a reversible complexation protection for free zinc and iron ions, preventing hydrolysis and precipitation during pH adjustment. Step S4, the cooling aging treatment, simulates low-temperature storage conditions by statically placing the product at 0-5℃, removing potential crystal nuclei and unstable complexes. Filtration with a 5-20 μm filter removes water-insoluble matter and large particle aggregates, ensuring that the water-insoluble matter content of the finished product does not exceed 0.2 wt%, meeting the stringent filtration requirements of drip irrigation systems. Continuous production processes ensure batch stability through online monitoring and automatic control, and temperature cycling tests verify the long-term stability of the finished product under actual storage and transportation conditions.

[0059] The synergistic effect of core-shell nanocomposite intermediate A and free fulvic acid in this invention is manifested in two aspects: structural complementarity and functional synergy. The core of core-shell nanocomposite intermediate A is a prepolymer P formed from ammonium polyphosphate and polyγ-glutamic acid, primarily acting as a slow-release carrier of phosphorus nutrients and a nanoparticle framework. The phosphate groups in the prepolymer form a hydrogen bond network with the carboxyl and hydroxyl groups of fulvic acid, providing anchoring points for the shell construction. Simultaneously, the steric hindrance effect and surface negative charge of the prepolymer inhibit nanoparticle aggregation and improve dispersion stability through electrostatic repulsion. The shell is formed by fulvic acid coating and in-situ complexation of zinc-iron salts, primarily playing a role in trace element immobilization, slow release, and activity protection. The multi-carboxyl and multi-hydroxyl structures of fulvic acid form multidentate complexes with zinc-iron ions. The complexed zinc-iron salts are slowly released in the rhizosphere microenvironment through ligand exchange or acid-catalyzed dissociation, significantly reducing the risk of hydrolysis and precipitation in high-phosphorus environments compared to free zinc sulfate and ferrous sulfate. Free fulvic acid focuses on solution phase stability and system viscosity regulation. It forms a dynamic protective layer through hydrogen bonding with the nanoparticle surface, creating a transition zone between the nanoparticle surface and the solution phase. This weakens the destructive effect of high ionic strength solutions on nanoparticle stability. Simultaneously, free fulvic acid forms weak hydrogen bonds with small molecules such as urea and ammonium nitrate, disrupting the hydrogen bond network formed under high concentration conditions, thereby reducing system viscosity. The synergistic mechanism between core-shell nanocomposite intermediate A and free fulvic acid lies in the core-shell structure enabling the nano-immobilization and sustained release of trace elements. Free fulvic acid, through a dual action, stabilizes the nanoparticles and regulates solution phase viscosity. Together, they construct a ternary synergistic stable network of nanoparticles, organic ligands, and inorganic salts. This achieves multiple objectives—low viscosity, low-temperature stability, and trace element enhancement—while ensuring high macro-element content, demonstrating a significant synergistic effect compared to single components.

[0060] Beneficial technical effects

[0061] 1. Significantly reduces viscosity and improves processing adaptability of high-nutrient formulations: Through the steric hindrance effect of core-shell nanocomposite intermediate A and the electrostatic shielding effect of its surface negative charge on free ions in the solution phase, as well as the disruptive effect of free fulvic acid on the hydrogen bond network of high-concentration inorganic salts, under high-nutrient formulation conditions of 15-22 wt% total nitrogen, 5-12 wt% total phosphorus, and 8-18 wt% total potassium, the viscosity at 25℃ can be controlled below 150 mPa·s, and the viscosity at the entire temperature range of -5℃ to 40℃ is no higher than 300 mPa·s. Compared with conventional formulations with the same nutrient content, the viscosity is reduced by 50-70%, enabling continuous pumping mixing and filterable filling, meeting the strict requirements of modern fertilizer production lines for low viscosity processability.

[0062] 2. Achieving full-temperature clarification and stability, and low-temperature anti-crystallization performance: The narrow particle size distribution of the core-shell nanoparticles (PDI not greater than 0.25) and the high surface charge (Zeta potential absolute value not less than 20mV) endow the nanoparticles with excellent dispersion stability. Free fulvic acid inhibits crystal nucleation and growth under low-temperature conditions through weak complexation with inorganic salts in the solution phase. The finished product showed no crystal precipitation or obvious stratification after standing at -5℃ for 7 days, and no visible crystal precipitation after standing in a sealed container at 0℃ for 7 days. After three temperature cycles from -5℃ to 40℃, the water-insoluble matter content increased by no more than 0.1 mass fraction points, which is significantly better than the problem of conventional high-nutrient water-soluble fertilizers easily crystallizing and stratifying under low-temperature conditions, ensuring the appearance quality and application uniformity of the product during winter storage and transportation.

[0063] 3. Achieving nanoscale immobilized slow-release and effective form preservation of trace elements zinc and iron: Zinc and iron salts are deposited in situ in the shell of core-shell nanocomposite intermediate A under the complexation of fulvic acid ligands. Zinc and iron in the shell account for 5-15 wt% of the dry basis mass of the nanoparticles. Zinc and iron existing in the shell form account for 30-100 wt% of the total zinc element and 30-100 wt% of the total iron element. The nanoshell protects zinc and iron ions from complexation precipitation by high phosphate in the solution phase through a dual mechanism of physical embedding and chemical complexation. The multidentate complex structure of fulvic acid achieves slow release in the rhizosphere microenvironment through ligand exchange or acid-catalyzed dissociation. Compared with free zinc sulfate and ferrous sulfate, the risk of hydrolysis and precipitation in high phosphorus environment is reduced by more than 60%, and the effectiveness of trace elements is improved by 40-50%, achieving slow-release enhancement and activity protection of trace elements.

[0064] 4. Synergistically enhancing the efficient utilization of nutrients and the effects of stress resistance and yield increase in winter wheat: The rational ratio of macronutrients nitrogen, phosphorus, and potassium, and the optimized design of the ammonium nitrogen to nitrate nitrogen mass ratio of 20-80:80-20, meet the differentiated needs of winter wheat for readily available and slowly available nitrogen during the greening, jointing, and grain-filling stages. Ammonium polyphosphate, as a phosphorus source, has both readily available and slowly available characteristics. Potassium nitrate and potassium sulfate synergistically provide potassium nutrients and supplement sulfur. Magnesium sulfate heptahydrate provides magnesium, a medium-level element. Humic acid, as a natural biostimulant, promotes root growth and nutrient absorption. Trace elements such as zinc and iron are continuously supplied during the critical growth period of winter wheat through a nano-slow-release mechanism, synergistically improving nutrient utilization efficiency, enhancing the resistance of winter wheat to stresses such as low temperature and drought, and promoting increased yield and quality.

[0065] 5. Ensuring batch stability and application safety: The preparation method employs multi-stage process control, including temperature-controlled dissolution, sequential feeding, shear dispersion, ultrasonic assistance, and cooling aging. Continuous production is achieved through online metering pumps, static mixers, and online pH and conductivity detection units. The batch-to-batch deviation of total nitrogen, total phosphorus, and total potassium mass fractions is controlled within ±5%. The finished product has a pH value of 5.5-7.0, close to neutral, with water-insoluble matter content not exceeding 0.2wt%, and conductivity of 15-40 mS / cm, meeting the requirements of drip irrigation systems for filtration and salt concentration, thus ensuring application safety and equipment compatibility. Attached Figure Description

[0066] Figure 1 This is a superimposed XRD pattern of Example 1, Comparative Example 6, and Comparative Example 8.

[0067] Figure 2 The image shows the intensity-weighted plots of DLS particle size distribution for Example 1 and Comparative Example 7.

[0068] Figure 3 The cumulative distribution of DLS is shown in Example 1 and Comparative Example 7.

[0069] Figure 4 The diagram shows the zeta potential distribution of Example 1 and Comparative Example 7.

[0070] Figure 5 The scatter plots of Zeta potentials versus mean and standard deviation are for Example 1 and Comparative Example 7.

[0071] Figure 6 The temperature-dependent viscosity curves are for Example 1, Comparative Example 2, and Comparative Example 4.

[0072] Figure 7 The turbidity-time diagrams for low-temperature crystallization kinetics of Example 1, Comparative Example 3, and Comparative Example 4 are shown.

[0073] Figure 8 The following is a time-varying diagram of the low-temperature crystallization kinetics of Example 1, Comparative Example 3, and Comparative Example 4.

[0074] Figure 9 This is a superimposed graph of the DSC curves of Example 1, Comparative Example 3, and Comparative Example 4. Detailed Implementation

[0075] 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.

[0076] Example 1

[0077] This embodiment provides a water-soluble fertilizer for stress resistance and yield increase in winter wheat, which is an aqueous solution using deionized water as a solvent, comprising the following components, based on the total mass of the finished product:

[0078] The total nitrogen in this embodiment is 18.5 wt%. The total nitrogen is provided by urea, ammonium nitrate, potassium nitrate, and ammonium polyphosphate. Urea provides 7.4 wt% nitrogen, accounting for 40 wt% of the total nitrogen; ammonium nitrate provides 6.51 wt% nitrogen; potassium nitrate provides 2.78 wt% nitrogen; and ammonium polyphosphate provides 1.81 wt% nitrogen while providing phosphorus. The mass ratio of ammonium nitrogen to nitrate nitrogen in this embodiment is 50:50, calculated based on the ammonium nitrogen provided by ammonium nitrate. Nitrogen provided by urea is not included in the calculation of the mass ratio of ammonium nitrogen to nitrate nitrogen in this embodiment.

[0079] In this embodiment, the total phosphorus nutrient content is converted to phosphorus pentoxide and is 8.5 wt%. The total phosphorus nutrient content in this embodiment is provided by ammonium polyphosphate.

[0080] In this embodiment, the total potassium nutrient content is converted to potassium oxide and is 13.0 wt%. The total potassium nutrient content in this embodiment is provided by potassium nitrate and potassium sulfate, wherein potassium nitrate provides 9.35 wt% potassium oxide and potassium sulfate provides 3.65 wt% potassium oxide.

[0081] This embodiment contains 2.5 wt% solids of core-shell nanocomposite intermediate A. The core of core-shell nanocomposite intermediate A in this embodiment is prepolymer P. Prepolymer P in this embodiment is a prepolymer formed by ammonium polyphosphate and polyγ-glutamic acid. The prepolymer P of this embodiment is prepared by the following steps: 125 parts by mass of ammonium polyphosphate are dissolved in deionized water at 60°C. The amount of deionized water added is such that the ammonium polyphosphate solution has a mass fraction of 25 wt% after dissolution, resulting in a homogeneous solution. Under continuous stirring, 12 parts by mass of polyγ-glutamic acid are added in batches over 60 minutes at 70°C, so that the mass ratio of ammonium polyphosphate to polyγ-glutamic acid is 125:12. Stirring is continued for 2 hours. The pH of the reaction solution is adjusted to 6.0 using a 30 wt% sodium hydroxide solution. The reaction solution is concentrated at 60°C under reduced pressure until the solid mass fraction is 37 wt%. In this embodiment, the reduced pressure is 8 kPa. When the viscosity of the prepolymer solution at 25°C is 1500 mPa·s, and the pH value changes by no more than 0.2 within 30 minutes under constant temperature at 25°C, the concentration is stopped, the solution is cooled, and insoluble matter is removed through a 100-mesh filter to obtain the prepolymer P of this embodiment.

[0082] The core-shell nanocomposite intermediate A of this embodiment is prepared by the following steps: Prepolymer P is taken and diluted with deionized water to a solid content of 18 wt%, and stirred at 40°C; based on the solid content of prepolymer P, 20 parts by mass of fulvic acid are added to the above solution based on 100 parts by mass of prepolymer P, and stirred at 40°C for 1 hour; a metal salt solution is prepared by dissolving zinc sulfate heptahydrate and ferrous sulfate heptahydrate in deionized water, controlling the molar ratio of zinc to iron to be 1:1. In this embodiment, the zinc ion concentration in the metal salt solution is 3 g / L, and the iron ion concentration is 3 g / L. The metal salt solution of this embodiment is stirred at 45°C for 60 minutes. The solution was added dropwise to the above system, and trisodium citrate dihydrate was added simultaneously to make the molar ratio of trisodium citrate dihydrate to zinc and iron 0.3:1. The pH was adjusted to 5.8 using a 30wt% sodium hydroxide solution, and stirring was continued for 2 hours. After the above steps, the reaction solution was subjected to high shear dispersion at 4500 rpm for 20 minutes, and then subjected to ultrasonic treatment at a frequency of 30 kHz and a sound power density of 1.0 W / cm² for 10 minutes. Large particles or gels were removed by filtration through a 3 μm filter to obtain a dispersion of core-shell nanocomposite intermediate A. In this embodiment, the nanoparticles in the dispersion have a D 50The core-shell nanocomposite intermediate A dispersion has a solid content of 15 wt% and a pH of 5.8. It contains 100 nm, has a PDI of 0.22, and the zinc and iron in the shell account for 9 wt% of the dry weight of the nanoparticles. No visible precipitation was observed after standing for 24 hours. The absolute value of the Zeta potential at 25°C is 25 mV. The core-shell nanocomposite intermediate D dispersion of this embodiment has a solid content of 15 wt% and a Zeta potential of 25 mV at 25°C. 50 PDI was determined by dynamic light scattering at 25°C.

[0083] This embodiment contains 0.5 wt% free fulvic acid. The free fulvic acid in this embodiment is fulvic acid added in addition to the fulvic acid contained in the core-shell nanocomposite intermediate A in this embodiment.

[0084] This embodiment contains magnesium sulfate heptahydrate, which is equivalent to 1.5 wt% magnesium oxide as a medium-level element.

[0085] This embodiment contains 0.3 wt% trisodium citrate dihydrate, which is used as a complexing agent.

[0086] In this embodiment, the total zinc content and the total iron content in the finished product are 0.10 wt%. Among them, 70 wt% of zinc and iron exist in the shell form of the core-shell nanocomposite intermediate A of this embodiment, accounting for 70 wt% of the total zinc content and 70 wt% of the total iron content. The remaining 30 wt% of zinc and iron exist in the free form of zinc sulfate heptahydrate and ferrous sulfate heptahydrate.

[0087] The remainder consists of deionized water and unavoidable impurities.

[0088] The water-soluble fertilizer for stress resistance and yield increase of winter wheat in this embodiment was prepared by the following method: 13.74 wt% deionized water was added to a reaction vessel, and then 12.14 wt% ammonium polyphosphate, 15.88 wt% urea, 18.59 wt% ammonium nitrate, 20.11 wt% potassium nitrate, 6.76 wt% potassium sulfate, and 9.20 wt% magnesium sulfate heptahydrate were added sequentially at 45°C. The mixture was stirred for 45 min until completely dissolved, with the solution being clear to the naked eye and free of visible solid particles as the criterion. At a reaction temperature of 35°C, a dispersion of core-shell nanocomposite intermediate A was added, so that the mass fraction of the solids of core-shell nanocomposite intermediate A in the finished product was 2.5 wt%. The mixture was stirred at a shear speed of 2000 rpm for 20 min, while simultaneously applying a sound power density of 30 kHz. The solution was treated with an ultrasonic field of 1.0 W / cm² for 10 min. At 30°C, 0.5 wt% free fulvic acid and 0.3 wt% trisodium citrate dihydrate were added, along with 0.13 wt% zinc sulfate heptahydrate and 0.15 wt% ferrous sulfate heptahydrate to replenish the free zinc and iron. The mixture was stirred for another 30 min, and the pH was adjusted to 6.3 using a 30 wt% sodium hydroxide solution. The resulting solution was cooled to 25°C and filtered through a 10 μm filter to remove water-insoluble matter. With a water-insoluble matter content of 0.15 wt%, the solution was subjected to a 3°C low-temperature standing aging process for 12 h to remove potential crystal nuclei, thereby improving the low-temperature storage stability of the finished product. Finally, the solution was filled and sealed to obtain the winter wheat stress-resistant and yield-increasing water-soluble fertilizer of this embodiment.

[0089] The viscosity of the water-soluble fertilizer in this embodiment is no higher than 280 mPa·s at any temperature within the temperature range of -5℃ to 40℃. The viscosity at 25℃ is 125 mPa·s. After standing for 7 days at -5℃, there is no crystallization or obvious stratification. The conductivity of the solution prepared at 25℃ with a mass fraction of 10 wt% is 26 mS / cm. No visible crystallization occurs after standing in a sealed container at 0℃ for 7 days. The water-insoluble matter content is 0.15 wt%, and the pH value is 6.3. The viscosity of this embodiment was measured using a rotational viscometer at 25℃.

[0090] Features of Example 1: This example uses a moderately balanced nutrient ratio, with total nitrogen (18.5 wt%), total phosphorus (8.5 wt%), and total potassium (13.0 wt%) at a mid-range level within the technical solution range. The mass ratio of ammonium nitrogen to nitrate nitrogen is a balanced 50:50. The core-shell nanocomposite intermediate A contains 2.5 wt% solids, 0.5 wt% free fulvic acid, 1.5 wt% magnesium oxide, and 0.10 wt% each of zinc and iron. This formulation parameter combination emphasizes stability and process controllability. The mass ratio of ammonium polyphosphate to polyγ-glutamic acid in prepolymer P is 125:12, concentrated to 37 wt% solids. The amount of fulvic acid used in the preparation of intermediate A is 20 parts by mass of the prepolymer P solids. Nanoparticles D... 50 The core-shell nanocomposite has a diameter of 100 nm, with zinc and iron accounting for 9 wt% of the dry basis in the shell. The finished product exhibits a viscosity of 125 mPa·s, electrical conductivity of 26 mS / cm, and a pH of 6.3 at 25℃. All performance indicators are at a moderate level, and the process parameters are mild, making it suitable for continuous production. Application scenario: This embodiment is suitable for conventional topdressing in the main winter wheat producing areas of the North China Plain, used from the greening stage to the jointing stage. It is recommended to dilute it 200-300 times for drip irrigation or foliar spraying. It can provide winter wheat with balanced nitrogen, phosphorus, and potassium nutrients. Simultaneously, the core-shell nanocomposite intermediate A improves nutrient utilization efficiency, and fulvic acid and polyγ-glutamic acid synergistically enhance cold and drought resistance. It is suitable for medium-fertility plots and yield-increasing needs under conventional climatic conditions.

[0091] Example 2

[0092] This embodiment provides a water-soluble fertilizer for stress resistance and yield increase in winter wheat, which is an aqueous solution using deionized water as a solvent, comprising the following components, based on the total mass of the finished product:

[0093] The total nitrogen in this embodiment is 20.0 wt%. The total nitrogen is provided by urea, ammonium nitrate, potassium nitrate, and ammonium polyphosphate. Urea provides 10.0 wt% nitrogen, accounting for 50 wt% of the total nitrogen; ammonium nitrate provides 4.8 wt% nitrogen; potassium nitrate provides 4.0 wt% nitrogen; and ammonium polyphosphate provides 1.2 wt% nitrogen along with phosphorus. The mass ratio of ammonium nitrogen to nitrate nitrogen in this embodiment is 50:50, calculated based on the ammonium nitrogen provided by ammonium nitrate. Nitrogen provided by urea is not included in the calculation of the mass ratio of ammonium nitrogen to nitrate nitrogen in this embodiment.

[0094] In this embodiment, the total phosphorus nutrient content of phosphorus pentoxide is converted to 6.0 wt%, and the total phosphorus nutrient content of this embodiment is provided by ammonium polyphosphate.

[0095] In this embodiment, the total potassium nutrient content is converted to potassium oxide and is 15.0 wt%. The total potassium nutrient content in this embodiment is provided by potassium nitrate and potassium sulfate, wherein potassium nitrate provides 13.5 wt% potassium oxide and potassium sulfate provides 1.5 wt% potassium oxide.

[0096] This embodiment contains 3.5 wt% solids of core-shell nanocomposite intermediate A. The core of core-shell nanocomposite intermediate A in this embodiment is prepolymer P. Prepolymer P in this embodiment is a prepolymer formed by ammonium polyphosphate and polyγ-glutamic acid. The prepolymer P of this embodiment is prepared by the following steps: 110 parts by mass of ammonium polyphosphate are dissolved in deionized water at 55°C. The amount of deionized water added is such that the ammonium polyphosphate solution has a mass fraction of 20 wt% after dissolution, resulting in a homogeneous solution. Under continuous stirring, 8 parts by mass of polyγ-glutamic acid are continuously added over 45 minutes at 65°C, so that the mass ratio of ammonium polyphosphate to polyγ-glutamic acid is 110:8. Stirring is continued for 1.5 hours. The pH of the reaction solution is adjusted to 5.8 using a 25 wt% sodium hydroxide solution. The reaction solution is concentrated at 55°C under reduced pressure until the solid mass fraction is 33 wt%. In this embodiment, the reduced pressure is 5 kPa. When the viscosity of the prepolymer solution at 25°C is 800 mPa·s and the pH value changes by no more than 0.2 within 30 minutes under constant temperature at 25°C, the concentration is stopped, the solution is cooled, and insoluble matter is removed through a 100-mesh filter to obtain the prepolymer P of this embodiment.

[0097] The core-shell nanocomposite intermediate A of this embodiment is prepared by the following steps: Prepolymer P is taken and diluted with deionized water to a solid content mass fraction of 15 wt%, and stirred at 38°C; based on the solid content of prepolymer P, 30 parts by mass of fulvic acid are added to the above solution based on 100 parts by mass of prepolymer P, and stirred at 38°C for 0.8 h; a metal salt solution is prepared by dissolving zinc sulfate heptahydrate and ferrous sulfate heptahydrate in deionized water, controlling the molar ratio of zinc to iron to be 1.5:1. In this embodiment, the zinc ion concentration in the metal salt solution is 5 g / L, and the iron ion concentration is 3.3 g / L. The metal salt solution of this embodiment is stirred at 42°C for 5 hours. The solution was added dropwise to the above system within 0 min, along with trisodium citrate dihydrate, to achieve a molar ratio of trisodium citrate dihydrate to zinc and iron of 0.25:1. The pH was adjusted to 5.5 using a 25 wt% sodium hydroxide solution, and stirring was continued for 1.5 h. After the above steps, the reaction solution was subjected to high shear dispersion at 3500 rpm for 15 min, followed by ultrasonic treatment at a frequency of 25 kHz and a sound power density of 0.8 W / cm² for 8 min. Large particles or gels were removed by filtration through a 2 μm filter to obtain a dispersion of core-shell nanocomposite intermediate A. In this embodiment, the nanoparticles in the dispersion have a D... 50The core-shell nanocomposite intermediate A dispersion has a solid content of 12 wt% and a pH of 5.5. It contains 80 nm, has a PDI of 0.20, and the zinc and iron content in the shell is 12 wt% of the dry weight of the nanoparticles. No visible precipitation was observed after standing for 24 hours. The absolute value of the Zeta potential at 25°C is 28 mV. The core-shell nanocomposite intermediate D dispersion of this embodiment has a solid content of 12 wt% and a Zeta potential of 28 mV at 25°C. 50 PDI was determined by dynamic light scattering at 25°C.

[0098] This embodiment contains 0.7 wt% free fulvic acid. The free fulvic acid in this embodiment is fulvic acid added in addition to the fulvic acid contained in the core-shell nanocomposite intermediate A in this embodiment.

[0099] This embodiment contains magnesium sulfate heptahydrate, which is equivalent to 2.0 wt% magnesium oxide as a medium-level element.

[0100] This embodiment contains 0.4 wt% trisodium citrate dihydrate, which is used as a complexing agent.

[0101] In this embodiment, the total zinc content in the finished product is 0.15 wt%, and the total iron content is 0.10 wt%. 80 wt% of the zinc and iron exist in the shell form of the core-shell nanocomposite intermediate A of this embodiment, accounting for 80 wt% of the total zinc content and 80 wt% of the total iron content. The remaining 20 wt% of the zinc and iron exist in the free form of zinc sulfate heptahydrate and ferrous sulfate heptahydrate.

[0102] The remainder consists of deionized water and unavoidable impurities.

[0103] The water-soluble fertilizer for stress resistance and yield increase of winter wheat in this embodiment was prepared by the following method: 10.85 wt% deionized water was added to a reaction vessel, and 8.57 wt% ammonium polyphosphate, 21.46 wt% urea, 13.71 wt% ammonium nitrate, 28.99 wt% potassium nitrate, 2.78 wt% potassium sulfate, and 12.27 wt% magnesium sulfate heptahydrate were added sequentially at 50°C. The mixture was stirred for 50 min until completely dissolved, with the solution being clear to the naked eye and free of visible solid particles as the criterion. When the reaction solution temperature was 38°C, a dispersion of core-shell nanocomposite intermediate A was added, so that the mass fraction of the solids of core-shell nanocomposite intermediate A in the finished product was 3.5 wt%. The mixture was stirred at a shear speed of 2200 rpm for 18 min, while simultaneously applying a sound power density of 25 kHz. The solution was treated with an ultrasonic field of 0.8 W / cm² for 8 min. At 28°C, 0.7 wt% free fulvic acid and 0.4 wt% trisodium citrate dihydrate were added, along with 0.13 wt% zinc sulfate heptahydrate and 0.10 wt% ferrous sulfate heptahydrate to replenish the free zinc and iron. The mixture was stirred for another 28 min, and the pH was adjusted to 6.0 using a 25 wt% sodium hydroxide solution. The resulting solution was cooled to 22°C and filtered through an 8 μm filter to remove water-insoluble matter. With a water-insoluble matter content of 0.12 wt%, the solution was subjected to a low-temperature aging process at 2°C for 8 h to remove potential crystal nuclei, thereby improving the low-temperature storage stability of the finished product. Finally, the solution was filled and sealed to obtain the winter wheat stress-resistant and yield-increasing water-soluble fertilizer of this embodiment.

[0104] The viscosity of the water-soluble fertilizer in this embodiment is no higher than 260 mPa·s at any temperature within the temperature range of -5℃ to 40℃. The viscosity at 25℃ is 110 mPa·s. After standing for 7 days at -5℃, there is no crystallization or obvious stratification. The conductivity of the solution prepared at 25℃ with a mass fraction of 10 wt% is 32 mS / cm. No visible crystallization occurs after standing in a sealed container at 0℃ for 7 days. The water-insoluble matter content is 0.12 wt%, and the pH value is 6.0. The viscosity of this embodiment was measured using a rotational viscometer at 25℃.

[0105] Features of Example 2: This example emphasizes a high nitrogen and potassium nutrient configuration. Total nitrogen (20.0 wt%) and total potassium (15.0 wt%) are both at a relatively high level within the technical range, while total phosphorus (6.0 wt%) is relatively low. Urea provides 50 wt% nitrogen, potassium nitrate provides 20 wt%, the core-shell nanocomposite intermediate A has a high solids content of 3.5 wt%, free fulvic acid (0.7 wt%), magnesium oxide (2.0 wt%), zinc (0.15 wt%), and iron (0.10 wt%). This formulation is biased towards promoting vegetative growth and improving stress resistance. The mass ratio of ammonium polyphosphate to polyγ-glutamic acid in prepolymer P is 110:8, concentrated to 33 wt% solids. The amount of fulvic acid used in the preparation of intermediate A is 30 parts by mass of the prepolymer P solids. The molar ratio of zinc to iron is 1.5:1. Nanoparticles D... 50 The core-shell nanocomposite has a diameter of 80 nm, with zinc and iron accounting for 12 wt% of the dry weight in the shell layer. 80% of the zinc and iron exist in the shell layer form. The finished product has a viscosity of 110 mPa·s, an electrical conductivity of 32 mS / cm, and a pH of 6.0 at 25℃, exhibiting characteristics of high nitrogen, high potassium, and high intermediate content. Application scenarios: This embodiment is particularly suitable for applications that require promoting the vegetative growth and tillering of winter wheat. It is recommended to use it from the jointing stage to the booting stage, diluted 150-250 times for drip irrigation. The high nitrogen and high potassium formula can quickly replenish nutrients, promote robust stems and ear differentiation. The high content of core-shell nanocomposite intermediate A and fulvic acid significantly improves nutrient absorption efficiency and stress resistance. It is suitable for rapid recovery of weak growth or after encountering adverse stresses such as late spring frost, as well as for plots with poor fertilizer retention capacity such as sandy soil. Use in the early grain-filling stage can promote grain filling and increase the thousand-grain weight.

[0106] Example 3

[0107] This embodiment provides a water-soluble fertilizer for stress resistance and yield increase in winter wheat, which is an aqueous solution using deionized water as a solvent, comprising the following components, based on the total mass of the finished product:

[0108] The total nitrogen in this embodiment is 16.5 wt%. The total nitrogen is provided by urea, ammonium nitrate, and ammonium polyphosphate. Urea provides 3.3 wt% nitrogen, accounting for 20 wt% of the total nitrogen, ammonium nitrate provides 11.7 wt% nitrogen, and ammonium polyphosphate provides 1.5 wt% nitrogen along with phosphorus. The mass ratio of ammonium nitrogen to nitrate nitrogen in this embodiment is 50:50, calculated based on the ammonium nitrogen provided by ammonium nitrate. Nitrogen provided by urea is not included in the calculation of the mass ratio of ammonium nitrogen to nitrate nitrogen in this embodiment.

[0109] In this embodiment, the total phosphorus nutrient content is converted to phosphorus pentoxide and is 10.0 wt%. The total phosphorus nutrient content in this embodiment is provided by ammonium polyphosphate.

[0110] In this embodiment, the total potassium nutrient content is calculated to be 10.0 wt% based on potassium oxide, and the total potassium nutrient content in this embodiment is provided by potassium sulfate.

[0111] This embodiment contains 1.5 wt% solids of core-shell nanocomposite intermediate A. The core of core-shell nanocomposite intermediate A in this embodiment is prepolymer P. Prepolymer P in this embodiment is a prepolymer formed by ammonium polyphosphate and polyγ-glutamic acid. The prepolymer P of this embodiment is prepared by the following steps: 140 parts by mass of ammonium polyphosphate are dissolved in deionized water at 65°C. The amount of deionized water added is such that the ammonium polyphosphate solution has a mass fraction of 32 wt% after dissolution, resulting in a homogeneous solution. Under continuous stirring, 16 parts by mass of polyγ-glutamic acid are added in batches over 90 minutes at 75°C, so that the mass ratio of ammonium polyphosphate to polyγ-glutamic acid is 140:16. Stirring is continued for 2.5 hours. The pH of the reaction solution is adjusted to 6.3 using a 35 wt% sodium hydroxide solution. The reaction solution is concentrated at 65°C under reduced pressure until the solid mass fraction is 42 wt%. In this embodiment, the reduced pressure is 12 kPa. When the viscosity of the prepolymer solution at 25°C is 2400 mPa·s, and the pH value changes by no more than 0.2 within 30 minutes under constant temperature at 25°C, the concentration is stopped, the solution is cooled, and insoluble matter is removed through a 100-mesh filter to obtain the prepolymer P of this embodiment.

[0112] The core-shell nanocomposite intermediate A of this embodiment is prepared by the following steps: Prepolymer P is taken and diluted with deionized water to a solid content of 22 wt%, and stirred at 43°C; based on the solid content of prepolymer P, 12 parts by mass of fulvic acid are added to the above solution based on 100 parts by mass of prepolymer P, and stirred at 43°C for 1.2 h; a metal salt solution is prepared by dissolving zinc sulfate heptahydrate and ferrous sulfate heptahydrate in deionized water, controlling the molar ratio of zinc to iron to be 0.8:1. In this embodiment, the zinc ion concentration in the metal salt solution is 2 g / L, and the iron ion concentration is 2.5 g / L. The metal salt solution of this embodiment is stirred at 50°C for 8 hours. The solution was added dropwise to the above system within 0 min, along with trisodium citrate dihydrate, to achieve a molar ratio of trisodium citrate dihydrate to zinc and iron of 0.4:1. The pH was adjusted to 6.2 using a 35 wt% sodium hydroxide solution, and stirring was continued for 2.5 h. After the above steps, the reaction solution was subjected to high shear dispersion at 5500 rpm for 25 min, followed by ultrasonic treatment at a frequency of 38 kHz and a sound power density of 1.3 W / cm² for 12 min. Large particles or gels were removed by filtration through a 4 μm filter to obtain a dispersion of core-shell nanocomposite intermediate A. In this embodiment, the nanoparticles in the dispersion have a D... 50The core-shell nanocomposite intermediate A dispersion has a density of 125 nm, a PDI of 0.24, and zinc and iron in the shell account for 7 wt% of the dry weight of the nanoparticles. The pH is 6.2, and no visible precipitation was observed after standing for 24 hours. The solid content of the dispersion is 20 wt%, and the absolute value of the Zeta potential at 25°C is 22 mV. The core-shell nanocomposite intermediate D dispersion of this embodiment... 50 PDI was determined by dynamic light scattering at 25°C.

[0113] This embodiment contains 0.3 wt% free fulvic acid. The free fulvic acid in this embodiment is fulvic acid added in addition to the fulvic acid contained in the core-shell nanocomposite intermediate A in this embodiment.

[0114] This embodiment contains magnesium sulfate heptahydrate, which is equivalent to 2.5 wt% magnesium oxide as a medium-level nutrient.

[0115] This embodiment contains 0.6 wt% trisodium citrate dihydrate, which is used as a complexing agent.

[0116] In this embodiment, the total zinc content in the finished product is 0.08 wt%, and the total iron content is 0.10 wt%. Among them, 50 wt% of zinc and iron exist in the shell form of the core-shell nanocomposite intermediate A of this embodiment, accounting for 50 wt% of the total zinc content and 50 wt% of the total iron content. The other 50 wt% of zinc and iron exist in the free form of zinc sulfate heptahydrate and ferrous sulfate heptahydrate.

[0117] The remainder consists of deionized water and unavoidable impurities.

[0118] The water-soluble fertilizer for stress resistance and yield increase of winter wheat in this embodiment was prepared by the following method: 17.28 wt% deionized water was added to a reaction vessel, and then 14.29 wt% ammonium polyphosphate, 7.08 wt% urea, 33.43 wt% ammonium nitrate, 18.52 wt% potassium sulfate, and 15.34 wt% magnesium sulfate heptahydrate were added sequentially at 55°C. The mixture was stirred for 55 min until completely dissolved, with the solution being clear to the naked eye and free of visible solid particles as the criterion. When the reaction solution temperature was 40°C, a dispersion of core-shell nanocomposite intermediate A was added, so that the mass fraction of the solids of core-shell nanocomposite intermediate A in the finished product was 1.5 wt%. The mixture was stirred at a shear speed of 2400 rpm for 25 min, while simultaneously applying a sound power density of 1.2 W / c at a frequency of 35 kHz. The solution was subjected to ultrasonic treatment in a m² area for 12 min. At 35°C, 0.3 wt% free fulvic acid and 0.6 wt% trisodium citrate dihydrate were added, along with 0.18 wt% zinc sulfate heptahydrate and 0.25 wt% ferrous sulfate heptahydrate to replenish the free zinc and iron. Stirring continued for 35 min, and the pH was adjusted to 6.5 using a 35 wt% sodium hydroxide solution. The mixed solution obtained in the above steps was cooled to 28°C and filtered through a 15 μm filter to remove water-insoluble matter. With a water-insoluble matter content of 0.18 wt%, the solution was subjected to low-temperature aging at 4°C for 18 h to remove potential crystal nuclei, thereby improving the low-temperature storage stability of the finished product. Finally, it was filled and sealed to obtain the winter wheat stress-resistant and yield-increasing water-soluble fertilizer of this embodiment.

[0119] The viscosity of the water-soluble fertilizer in this embodiment is no higher than 295 mPa·s at any temperature within the temperature range of -5℃ to 40℃. The viscosity at 25℃ is 140 mPa·s. After standing for 7 days at -5℃, there is no crystallization or obvious stratification. The conductivity of the solution prepared at 25℃ with a mass fraction of 10 wt% is 22 mS / cm. No visible crystallization occurs after standing in a sealed container at 0℃ for 7 days. The water-insoluble matter content is 0.18 wt%, and the pH value is 6.5. The viscosity of this embodiment was measured using a rotational viscometer at 25℃.

[0120] Features of Example 3: This example emphasizes the configuration of phosphate fertilizer and medium-level elements. Total phosphorus (10.0 wt%) is at a relatively high level within the technical range, total nitrogen (16.5 wt%) is relatively low, total potassium (10.0 wt%) is moderate, urea provides only 20 wt% of nitrogen, which is at the lower limit, ammonium nitrate provides a relatively high proportion of nitrogen, potassium is entirely provided by potassium sulfate (no potassium nitrate), magnesium oxide (2.5 wt%) is relatively high, core-shell nanocomposite intermediate A has a relatively low solid content of 1.5 wt%, free fulvic acid (0.3 wt%), zinc (0.08 wt%), iron (0.10 wt%), and trisodium citrate dihydrate (0.6 wt%) are relatively high. This formula is biased towards promoting reproductive growth and improving grain quality. The mass ratio of ammonium polyphosphate to polyγ-glutamic acid in prepolymer P is 140:16, concentrated to 42 wt% solids. The amount of fulvic acid used in the preparation of intermediate A is 12 parts by mass of the prepolymer P solids. The molar ratio of zinc to iron is 0.8:1. Nanoparticle D... 50 The sample has a diameter of 125 nm, with zinc and iron accounting for 7 wt% of the dry weight in the shell layer, and 50% of the zinc and iron existing in the shell layer form. The finished product has a viscosity of 140 mPa·s at 25℃, an electrical conductivity of 22 mS / cm, and a pH of 6.5, exhibiting overall characteristics of high phosphorus, high magnesium, low nitrogen, and low intermediate content. Application scenario: This embodiment is particularly suitable for improving the quality of winter wheat in the later stages of growth. It is recommended to use it from the grain-filling stage to maturity, diluted 250-350 times for foliar spraying or drip irrigation. The high phosphorus formula promotes grain filling and protein synthesis, the higher magnesium content helps chlorophyll synthesis and photosynthesis, the use of potassium sulfate can improve grain quality, and the lower intermediate A content reduces costs while meeting basic stress resistance requirements. It is suitable for fields with relatively low phosphorus and potassium in the soil or for producing high-quality strong gluten wheat. Using it 20-30 days before maturity can significantly improve protein content and gluten quality, making it suitable for the production of high-quality specialty wheat.

[0121] Example 4

[0122] This embodiment provides a water-soluble fertilizer for stress resistance and yield increase in winter wheat, which is an aqueous solution using deionized water as a solvent, comprising the following components, based on the total mass of the finished product:

[0123] The total nitrogen in this embodiment is 21.0 wt%. The total nitrogen is provided by urea, ammonium nitrate, potassium nitrate, and ammonium polyphosphate. Urea provides 12.0 wt% nitrogen, accounting for 57 wt% of the total nitrogen; ammonium nitrate provides 2.1 wt% nitrogen; potassium nitrate provides 5.3 wt% nitrogen; and ammonium polyphosphate provides 1.6 wt% nitrogen along with phosphorus. The mass ratio of ammonium nitrogen to nitrate nitrogen in this embodiment is calculated as 50:50 based on the ammonium nitrogen provided by ammonium nitrate. Nitrogen provided by urea is not included in the calculation of the mass ratio of ammonium nitrogen to nitrate nitrogen in this embodiment.

[0124] In this embodiment, the total phosphorus nutrient content is converted to phosphorus pentoxide and is 11.0 wt%. The total phosphorus nutrient content in this embodiment is provided by ammonium polyphosphate.

[0125] In this embodiment, the total potassium nutrient content is converted to potassium oxide and is 9.0 wt%. The total potassium nutrient content in this embodiment is provided by potassium nitrate and potassium sulfate, wherein potassium nitrate provides 7.9 wt% potassium oxide and potassium sulfate provides 1.1 wt% potassium oxide.

[0126] This embodiment contains 4.5 wt% solids of core-shell nanocomposite intermediate A. The core of core-shell nanocomposite intermediate A in this embodiment is prepolymer P. Prepolymer P in this embodiment is a prepolymer formed by ammonium polyphosphate and polyγ-glutamic acid. The prepolymer P of this embodiment is prepared by the following steps: 148 parts by mass of ammonium polyphosphate are dissolved in deionized water at 68°C. The amount of deionized water added is such that the ammonium polyphosphate solution has a mass fraction of 38 wt% after dissolution, resulting in a homogeneous solution. Under continuous stirring, 19 parts by mass of polyγ-glutamic acid are added in batches over 110 minutes at 78°C, so that the mass ratio of ammonium polyphosphate to polyγ-glutamic acid is 148:19. Stirring is continued for 2.8 hours. The pH of the reaction solution is adjusted to 6.5 using a 38 wt% sodium hydroxide solution. The reaction solution is concentrated at 68°C under reduced pressure until the solid mass fraction is 44 wt%. In this embodiment, the reduced pressure is 18 kPa. When the viscosity of the prepolymer solution at 25°C is 2800 mPa·s, and the pH value changes by no more than 0.2 within 30 minutes under constant temperature at 25°C, the concentration is stopped, the solution is cooled, and insoluble matter is removed through a 100-mesh filter to obtain the prepolymer P of this embodiment.

[0127] The core-shell nanocomposite intermediate A of this embodiment is prepared by the following steps: Prepolymer P is taken and diluted with deionized water to a solids mass fraction of 12 wt%, and stirred at 36°C; based on the solids of prepolymer P, 38 parts by mass of fulvic acid are added to the above solution per 100 parts by mass of prepolymer P, and stirred at 36°C for 0.6 h; a metal salt solution is prepared by dissolving zinc sulfate heptahydrate and ferrous sulfate heptahydrate in deionized water, controlling the molar ratio of zinc to iron to be 2.5:1. In this embodiment, the zinc ion concentration in the metal salt solution is 8 g / L, and the iron ion concentration is 3.2 g / L. The metal salt solution of this embodiment is stirred at 52°C for 100 h. The solution was added dropwise to the above system within min, while simultaneously adding trisodium citrate dihydrate to achieve a molar ratio of trisodium citrate dihydrate to total zinc and iron of 0.15:1. The pH was adjusted to 5.2 using a 38wt% sodium hydroxide solution, and stirring was continued for 1.2 h. After the above steps, the reaction solution was subjected to high shear dispersion at 5800 rpm for 28 min, followed by ultrasonic treatment at a frequency of 38 kHz and a sound power density of 1.4 W / cm² for 14 min. Large particles or gels were removed by filtration through a 1.5 μm filter to obtain a dispersion of core-shell nanocomposite intermediate A. In this embodiment, the nanoparticles in the dispersion have a D 50 The core-shell nanocomposite intermediate A dispersion has a solid content of 10 wt% and a pH of 5.2. It contains 65 nm, a PDI of 0.18, and zinc and iron in the shell constitute 14 wt% of the dry weight of the nanoparticles. No visible precipitation was observed after standing for 24 hours. The absolute value of the Zeta potential at 25°C is 32 mV. The core-shell nanocomposite intermediate D dispersion of this embodiment has a solid content of 10 wt% and a solid content of 10 wt%. 50 PDI was determined by dynamic light scattering at 25°C.

[0128] This embodiment contains 0.15 wt% free fulvic acid. The free fulvic acid in this embodiment is fulvic acid added in addition to the fulvic acid contained in the core-shell nanocomposite intermediate A in this embodiment.

[0129] This embodiment contains magnesium sulfate heptahydrate, which is equivalent to 0.6 wt% magnesium oxide as a medium-level element.

[0130] This embodiment contains 0.15 wt% trisodium citrate dihydrate, which is used as a complexing agent.

[0131] In this embodiment, the total zinc content in the finished product is 0.18 wt%, and the total iron content is 0.08 wt%. Among them, 90 wt% of zinc and iron exist in the shell form of the core-shell nanocomposite intermediate A of this embodiment, accounting for 90 wt% of the total zinc content and 90 wt% of the total iron content. The remaining 10 wt% of zinc and iron exist in the free form of zinc sulfate heptahydrate and ferrous sulfate heptahydrate.

[0132] The remainder consists of deionized water and unavoidable impurities.

[0133] The water-soluble fertilizer for stress resistance and yield increase of winter wheat in this embodiment was prepared by the following method: 8.52 wt% deionized water was added to a reaction vessel, and 15.71 wt% ammonium polyphosphate, 25.75 wt% urea, 6.00 wt% ammonium nitrate, 38.41 wt% potassium nitrate, 2.04 wt% potassium sulfate, and 3.68 wt% magnesium sulfate heptahydrate were added sequentially at 32°C. The mixture was stirred for 32 min until completely dissolved, with the solution being clear to the naked eye and free of visible solid particles as the criterion. When the reaction solution temperature was 27°C, a dispersion of core-shell nanocomposite intermediate A was added, so that the mass fraction of solids of core-shell nanocomposite intermediate A in the finished product was 4.5 wt%. The mixture was stirred at a shear speed of 2800 rpm for 28 min, while simultaneously applying a sound power density of 1 at a frequency of 38 kHz. The solution was treated with an ultrasonic field of 4 W / cm² for 14 min. At 22°C, 0.15 wt% free fulvic acid and 0.15 wt% trisodium citrate dihydrate were added, along with 0.08 wt% zinc sulfate heptahydrate and 0.04 wt% ferrous sulfate heptahydrate to replenish the free zinc and iron. The mixture was stirred for another 22 min, and the pH was adjusted to 5.7 using a 38 wt% sodium hydroxide solution. The resulting mixed solution was cooled to 18°C ​​and filtered through a 6 μm filter to remove water-insoluble matter. With a water-insoluble matter content of 0.08 wt%, the solution was subjected to a 20-hour cooling aging process at 1°C to remove potential crystal nuclei, thereby improving the low-temperature storage stability of the finished product. Finally, the solution was filled and sealed to obtain the winter wheat stress-resistant and yield-increasing water-soluble fertilizer of this embodiment.

[0134] The viscosity of the water-soluble fertilizer in this embodiment is no higher than 220 mPa·s at any temperature within the temperature range of -5℃ to 40℃. The viscosity at 25℃ is 95 mPa·s. After standing for 7 days at -5℃, there is no crystallization or obvious stratification. The conductivity of the solution prepared at 25℃ with a mass fraction of 10 wt% is 37 mS / cm. No visible crystallization occurs after standing in a sealed container at 0℃ for 7 days. The water-insoluble matter content is 0.08 wt%, and the pH value is 5.7. The viscosity of this embodiment was measured using a rotational viscometer at 25℃.

[0135] Example 4 Features: This example uses a high-nitrogen, high-phosphorus, and low-potassium nutrient ratio, with total nitrogen 21.0 wt%, total phosphorus 11.0 wt%, and total potassium 9.0 wt%. Urea provides 57 wt% nitrogen, potassium nitrate provides 25% of the total nitrogen, core-shell nanocomposite intermediate A has a solid content of 4.5 wt%, free fulvic acid 0.15 wt%, magnesium oxide 0.6 wt%, trisodium citrate dihydrate 0.15 wt%, zinc 0.18 wt%, and iron 0.08 wt%. The mass ratio of ammonium polyphosphate to polyγ-glutamic acid in prepolymer P is 148:19, concentrated to 44 wt% solids. The prepolymer solution viscosity is 2800 mPa·s. Prepolymer P is diluted to 12 wt% during the preparation of intermediate A. The amount of fulvic acid used is 38 parts by mass. The molar ratio of zinc to iron is 2.5:1, the molar ratio of trisodium citrate to total zinc and iron is 0.15:1, the zinc ion concentration of the metal salt solution is 8 g / L, and nanoparticles D... 50 The core-shell structure contains 65 nm of zinc and iron, with zinc and iron accounting for 14 wt% of the dry basis weight. 90% of the zinc and iron exist in the shell form. The finished product is prepared at a relatively low temperature. At 25℃, the viscosity is 95 mPa·s, the conductivity is 37 mS / cm, the pH value is 5.7, and the water-insoluble matter is 0.08 wt%. This formulation exhibits the characteristics of high total nitrogen, high total phosphorus, high intermediate content, and high zinc content. At the same time, the content of free humic acid and magnesium oxide is low. The zinc and iron encapsulation ratio in the core-shell structure reaches 90%. The nanoparticle size is small at 65 nm, and the finished product has low viscosity and good flowability.

[0136] Application Scenarios: This embodiment is suitable for special application scenarios requiring high-intensity and rapid nutrient replenishment. It is recommended for emergency remediation after winter wheat suffers severe low-temperature freezing damage or drought stress. Dilute 100-200 times for foliar spraying or drip irrigation. The extremely high total nitrogen and core-shell nanocomposite intermediate A content can quickly restore plant growth vigor. The high proportion of urea and potassium nitrate provides a continuous nitrogen source. The high total phosphorus promotes root recovery and energy metabolism. The high zinc content helps hormone synthesis and the recovery of stress resistance. The low magnesium content and free fulvic acid reduce costs. The extremely high intermediate A solids content significantly improves nutrient utilization and stress resistance. It is suitable for emergency application when encountering extreme adversity during the critical growth period, as well as for enhanced nutrient regulation in saline-alkali land or severely nutrient-deficient plots.

[0137] Comparative Example 1: It is basically the same as Example 1, except that the solid content of the core-shell nanocomposite intermediate A is 0.3 wt%, while the amount of other components and preparation conditions remain unchanged.

[0138] Comparative Example 2: It is basically the same as Example 1, except that the solid content of the core-shell nanocomposite intermediate A is 5.5 wt%, while the amount of other components and the preparation conditions remain unchanged.

[0139] Comparative Example 3: It is basically the same as Example 1, except that the total nitrogen content is 13.0 wt% (achieved by reducing the amount of urea and ammonium nitrate), while the amount of other components and preparation conditions remain unchanged.

[0140] Comparative Example 4: It is basically the same as Example 1, except that the mass ratio of ammonium nitrogen to nitrate nitrogen is 10:90 (achieved by adjusting the relative ratio of ammonium nitrogen to nitrate nitrogen in ammonium nitrate), while the amount of other components and preparation conditions remain unchanged.

[0141] Comparative Example 5: It is basically the same as Example 1, except that free fulvic acid is not added, while the amounts of other components and preparation conditions remain unchanged.

[0142] Comparative Example 6: It is basically the same as Example 1, except that the mass ratio of ammonium polyphosphate to polyγ-glutamic acid is 125:3 (the amount of polyγ-glutamic acid is reduced to 3 parts by mass) when preparing prepolymer P, while the amount of other components and preparation conditions remain unchanged.

[0143] Comparative Example 7: It is basically the same as Example 1, except that the high-shear dispersion and ultrasonic treatment steps are not performed when preparing core-shell nanocomposite intermediate A. The dispersion of intermediate A is obtained directly by filtration. The amount of other components and the preparation conditions remain unchanged.

[0144] Comparative Example 8: It is basically the same as Example 1, except that the amount of fulvic acid used in the preparation of core-shell nanocomposite intermediate A is 3 parts by mass of the prepolymer P solids, while the amounts of other components and preparation conditions remain unchanged.

[0145] Performance testing:

[0146] Viscosity performance test

[0147] Test Subject: The finished product of the winter wheat stress-resistant and yield-increasing water-soluble fertilizer in this embodiment. Test Objective: To evaluate the rheological properties and pumpability of the water-soluble fertilizer at different temperatures. Test Principle: The viscosity change of a liquid under shear stress is measured using a rotational viscometer. Viscosity is a physical quantity that hinders flow within a liquid and directly affects the pumpability, mixing, and filling operability of the product. Experimental Method: Using an NDJ-8S rotational viscometer, 100 mL of sample was placed in a constant temperature water bath and equilibrated for 30 min at -5℃, 0℃, 25℃, and 40℃ respectively. Viscosity was measured using a No. 2 rotor at 60 rpm. Each temperature point was tested three times, and stable readings were recorded. Key Parameters: Test temperature range -5℃ to 40℃, temperature control accuracy ±0.5℃, rotor speed 60 rpm, measurement time 60 s. Data Processing: The average and standard deviation of viscosity at different temperatures were calculated to evaluate the smoothness of the viscosity-temperature curve. Lower viscosity and lower temperature sensitivity indicate better processing suitability.

[0148] Low-temperature storage stability test

[0149] Test object: The finished product of water-soluble fertilizer for winter wheat stress resistance and yield increase in this embodiment. Test purpose: To evaluate the crystallization precipitation and stratification stability of the water-soluble fertilizer under low-temperature conditions. Test principle: The solubility of high-concentration inorganic salt solutions decreases at low temperatures, making it easy to form crystal nuclei. By observing the crystallization precipitation and stratification phenomena through low-temperature static observation, the low-temperature stability of the formulation is evaluated. Experimental method: Take 500 mL of the sample and put it into a transparent glass bottle. After sealing, place it in a constant-temperature oven at -5°C for 7 days. Observe and record the crystallization precipitation, stratification, and solution clarity every 24 hours. After 7 days, take out the sample and restore it to 25°C, and detect the changes in the content of water-insoluble substances and the content of main nutrients. Key parameters: Test temperature -5°C ± 1°C, static time 7 days, observation frequency once every 24 hours. Data processing: Record the crystallization precipitation time point, stratification degree, and the increment of water-insoluble substance content. If there is no visible crystal to the naked eye and the increment of water-insoluble substance is <0.1 wt%, it is judged as qualified.

[0150] Test for the retention performance of available zinc and iron

[0151] Test object: The dispersion liquid of core-shell nano-composite intermediate A and the finished product water-soluble fertilizer in this embodiment. Test purpose: To evaluate the solid loading and slow-release performance of core-shell structure on zinc and iron trace elements and the ability to maintain the effective form. Test principle: The content of available zinc and iron is determined by EDTA chelation titration method. The ratio of shell-encapsulated state to free state is determined by centrifugal separation. The slow-release performance is evaluated by pH gradient release experiment. Experimental method: Take the dispersion liquid of core-shell nano-composite intermediate A, centrifuge it at 10000 rpm for 30 min to separate the nanoparticles and the supernatant. Measure the zinc and iron content in the precipitate and the supernatant respectively to calculate the encapsulation rate. Prepare buffer solutions with pH values of 4.5, 5.5, 6.5, and 7.5. Dilute the dispersion liquid of intermediate A at a ratio of 1:100, and measure the zinc and iron content released into the solution after standing at 25°C for 24 h to calculate the cumulative release rate. Key parameters: Centrifugal speed 10000 rpm, centrifugal time 30 min, pH gradient of buffer solution, release temperature 25°C, release time 24 h. Data processing: Calculate the encapsulation rate and the cumulative release rate at different pH values, draw the release curve. If the encapsulation rate > 60% and the release rate within the range of pH 5.5 - 7.5 < 30%, it indicates good slow-release performance.

[0152] Conductivity test

[0153] Test Subject: The winter wheat stress-resistance and yield-increasing water-soluble fertilizer in this embodiment was prepared as a 10wt% diluted solution. Test Objective: To evaluate the ionic strength and nutrient availability of the water-soluble fertilizer. Test Principle: Conductivity reflects the ion concentration and migration ability in a solution. The conductivity of high-nutrient water-soluble fertilizers is closely related to nutrient content, ion form, and compatibility stability. Experimental Method: Accurately weigh 10.0g of the water-soluble fertilizer sample, dilute to 100mL with deionized water, equilibrate in a 25℃ constant temperature water bath for 30min, and measure the conductivity using a DDS-307 conductivity meter. Calibration was performed using a standard conductivity solution (12.88mS / cm) before the test. Each sample was measured three times. Key Parameters: Sample concentration 10wt%, test temperature 25℃±0.2℃, conductivity meter calibration standard solution 12.88mS / cm. Data processing: Calculate the average conductivity and standard deviation. A conductivity range of 15-40 mS / cm indicates a suitable ion concentration. Too high a conductivity can easily cause salt damage, while too low a conductivity indicates insufficient nutrient content.

[0154] Water-insoluble matter content test

[0155] Test Subject: The finished product of the winter wheat stress-resistance and yield-increasing water-soluble fertilizer in this embodiment. Test Objective: To evaluate the filterability and clarity of the water-soluble fertilizer to ensure it meets the requirements for use in irrigation systems. Test Principle: Water-insoluble matter includes incompletely dissolved raw materials, precipitates and gels generated during the reaction process, etc. Its content is determined by filtration with quantitative filter paper and drying and weighing. Experimental Method: 100g of sample was diluted with 400mL of deionized water and stirred thoroughly for 10min. The sample was then filtered through quantitative filter paper with a pore size of 0.45μm. The residue was rinsed three times with a small amount of deionized water. The filter paper and residue were placed in a 105℃ oven and dried to constant weight. After cooling, the sample was weighed, and the mass fraction of water-insoluble matter was calculated. Key Parameters: Dilution ratio 1:5, stirring time 10min, filter paper pore size 0.45μm, drying temperature 105℃, constant weight criterion: the difference between two consecutive weighings <0.5mg. Data Processing: The mass fraction of water-insoluble matter was calculated. For n=3 samples, the average value was taken. Water-insoluble matter ≤0.2wt% meets the requirements for drip irrigation fertilization.

[0156] Characterization of core-shell nanoparticle size distribution and zeta potential

[0157] Test Object: The dispersion of core-shell nanocomposite intermediate A in this embodiment. Test Objective: To characterize the particle size distribution, dispersion uniformity, and surface charge stability of the nanoparticles. Test Principle: Dynamic light scattering (DLS) was used to determine the hydrodynamic diameter and polydispersity index (PDI) of the nanoparticles. The Zeta potential reflects the contribution of the particle surface charge to the dispersion stability. Experimental Method: The dispersion of core-shell nanocomposite intermediate A was diluted 100 times with deionized water to a suitable concentration. The particle size distribution D was measured using a Malvern Zetasizer Nano ZS90 laser particle size analyzer at 25°C and a scattering angle of 90°.50 The Zeta potential was determined using electrophoretic light scattering mode, with each sample measured three times and the average value taken. Key parameters: dilution factor 100-fold, test temperature 25℃, scattering angle 90°, refractive index set to 1.45, and medium viscosity 0.89 mPa·s. Data processing: Record D... 50 D 10 D 90 And PDI value, calculate the mean and standard deviation of Zeta potential, D 50 A wavelength of 50-150 nm, a PDI < 0.25, and an absolute value of the Zeta potential > 20 mV indicate good dispersibility and stability.

[0158] Figure 1 The XRD patterns of Example 1, Comparative Example 6, and Comparative Example 8 are overlaid. The parameters were fixed: scanning angle range of 5° to 80° with a step size of 0.02°, the same instrument conditions, and the same data processing flow. The diffraction intensity (CPS) was used as the ordinate. The varying parameters were the changes in sample formulation and structural state between Example 1, Comparative Example 6, and Comparative Example 8. The spectrum of Example 1 exhibits a more stable, broad, diffuse peak accompanied by several characteristic peaks with continuous peak shapes, indicating a more balanced phase state and microscopic order. Comparative Examples 6 and 8 show sharper peak shapes or additional peak shape differences at several angles, indicating a more pronounced tendency for crystallization or phase separation, leading to a decrease in structural consistency. This demonstrates that Example 1 is superior in terms of phase structure stability and uniformity, thus supporting the reproducibility and reliability of the scheme.

[0159] Figure 2 The DLS particle size distribution intensity weighted plots for Example 1 and Comparative Example 7 are shown. With the same measurement method and data caliber fixed, particle size (nm) is plotted on the x-axis using a logarithmic scale, and the percentage of intensity distribution is plotted on the y-axis, under the same dispersion and detection conditions. Variations are the changes in the sample system between Example 1 and Comparative Example 7, reflected in the differences in the particle size distribution center and width. The distribution peaks in Example 1 are concentrated, with a core of approximately 100 nm D50 and a narrower distribution. The distribution peaks in Comparative Example 7 are significantly shifted to the right, with a core of approximately 280 nm D50 and a wider distribution. This indicates that Example 1 can form smaller and more concentrated particle size clusters, while Comparative Example 7 is more prone to large particles and distribution expansion. This demonstrates that Example 1 has stronger dispersion stability and particle size controllability, meeting the requirements for correct particle size control in the protocol.

[0160] Figure 3The DLS cumulative distribution plots for Example 1 and Comparative Example 7 are shown. The parameters are fixed at the same DLS data caliber, with the particle size (nm) on the x-axis and the cumulative distribution percentage on the y-axis, maintaining a monotonically increasing cumulative distribution. The varying parameters are the differences in the rising range and slope of the cumulative distribution curves between Example 1 and Comparative Example 7. In Example 1, the cumulative distribution rises rapidly in the smaller particle size range and approaches 100% earlier. In Comparative Example 7, the rising range shifts towards the larger particle size side and the rise is slower. This indicates that Example 1 has a smaller overall particle size and a more concentrated population, while Comparative Example 7 exhibits a more significant large-particle-size tail and distribution dispersion. This demonstrates that Example 1 better meets the scheme's objectives in terms of particle size uniformity and process stability, thus verifying the effectiveness of the scheme.

[0161] Figure 4 The zeta potential distribution diagrams for Example 1 and Comparative Example 7 are shown. With the same test method and data caliber fixed, the zeta potential (mV) is plotted on the x-axis and frequency percentage on the y-axis, under the same medium and measurement conditions. The varying parameters represent the differences in the potential distribution center and dispersion between Example 1 and Comparative Example 7. The distribution center in Example 1 is approximately -25 mV and more concentrated, while the distribution center in Comparative Example 7 is approximately -12 mV and more dispersed. This indicates that Example 1 has a higher surface charge intensity and a more stable interfacial electrical state, which is more conducive to suppressing particle aggregation and improving the stability of the dispersed system. This proves that the stabilization mechanism of Example 1 is more sufficient and supports the correctness of the scheme.

[0162] Figure 5 The scatter plots of Zeta potentials and their mean and standard deviation are shown for Example 1 and Comparative Example 7. With fixed parameters, each sample underwent parallel testing (n=3), and the same statistical caliber was used to output the mean and standard deviation. The comparison samples were Example 1 and Comparative Example 7. The varying parameters represent differences in the mean and dispersion of the Zeta potentials due to different sample systems. The scatter plots of Example 1 cluster around approximately -25 mV with a smaller standard deviation, while the scatter plots of Comparative Example 7 cluster around approximately -12 mV with greater fluctuations. This indicates that Example 1 has a more consistent electrical state and better intra-batch repeatability, while Comparative Example 7 exhibits weaker stability and consistency. This demonstrates that Example 1 has more reliable repeatability in key interface indicators, further validating the correctness and stability of the scheme.

[0163] Figure 6The figures show the temperature-dependent viscosity curves of Examples 1, 2, and 4. The fixed parameters were a shearing condition of 60 rpm and temperatures of -5°C, 0°C, 25°C, and 40°C. Parallel testing and error bars were used to characterize the dispersion. The varying parameters were the differences in viscosity levels and temperature sensitivity of the sample systems at different temperatures. Example 1 showed a viscosity of approximately 125 mPa·s near 25°C, which decreased reasonably with increasing temperature while maintaining a small error. Comparative Example 2 showed a significantly higher viscosity (approximately 245 mPa·s) under the same conditions and was generally more viscous. Comparative Example 4 showed even higher viscosity at lower temperatures and exhibited a stronger tendency to thicken at low temperatures. This indicates that Example 1 achieves a better balance between room temperature processability and low-temperature fluidity, and is more conducive to obtaining stable preparation and usage performance. This demonstrates that the system design of Example 1 can achieve controllable viscosity and temperature adaptability, thus supporting the correctness of the scheme.

[0164] Figure 7 The turbidity-time graphs for low-temperature crystallization kinetics of Examples 1, 3, and 4 are shown. The fixed parameters were temperature -5°C and observation time from 0 h to 168 h. Turbidity NTU was used to characterize the low-temperature precipitation and crystallization process. The varying parameters were the differences in the induction period, growth rate, and final turbidity level of the sample system across Examples 1, 3, and 4. Example 1 maintained a low turbidity level and slow change throughout the entire time range, indicating that precipitation or crystallization was effectively suppressed at low temperatures. Comparative Example 3 showed a more significant increase in turbidity, accelerating in the middle and later stages. Comparative Example 4 showed a rapid increase earlier and a higher final turbidity, indicating insufficient low-temperature stability and a greater susceptibility to phase transitions or crystallization. This demonstrates that Example 1 is superior in terms of low-temperature storage stability, thus verifying that the scheme can effectively improve low-temperature phase stability and system reliability.

[0165] Figure 8 The graphs show the crystallization amount over time in the low-temperature crystallization kinetics of Examples 1, 3, and 4. The parameters were fixed at -5°C for 0 h to 168 h, with the crystallization process characterized by a percentage increase in crystallization amount. The curves showed a monotonically increasing trend. The varying parameters represented the differences in the rate of increase in crystallization amount and the time taken to reach a high crystallization amount among Examples 1, 3, and 4. In Example 1, the crystallization amount remained close to zero or increased slowly over a long period, indicating a significant weakening of the crystallization driving force. In Comparative Example 3, the crystallization amount gradually increased and approached a relatively high level in the later stages. In Comparative Example 4, the crystallization amount increased earlier and rapidly, approaching the high crystallization range, indicating that it was more prone to crystallization and caused fluctuations in system structure and performance. This demonstrates that Example 1 can effectively reduce the risk of low-temperature crystallization and improve storage stability, supporting the correctness of the scheme regarding the low-temperature stabilization effect.

[0166] Figure 9The above is a superimposed DSC curve of Example 1, Comparative Example 3, and Comparative Example 4. The parameters were fixed under the same differential scanning calorimetry conditions, with heat flux (W / g) as the ordinate and temperature (°C) as the abscissa. The comparison samples were Example 1, Comparative Example 3, and Comparative Example 4. The varying parameters were the differences in peak position, peak area, and peak shape of thermal events caused by differences in the sample systems. The exothermic or endothermic characteristic peaks of Example 1 were weaker or closer to the low-influence region, indicating that potential phase transitions or crystallization thermal events were suppressed and the thermal behavior was smoother. Comparative Examples 3 and 4 showed more obvious characteristic peaks with higher peak intensities, indicating that they were more prone to crystallization or phase transitions accompanied by more significant thermal effects. Combined with the low-temperature kinetic results, this mutually corroborates the better phase stability of Example 1, proving that Example 1 is more consistent in terms of thermal behavior and phase stability, thus verifying the correctness of the scheme and the self-consistency of the stabilization mechanism.

[0167] As can be seen from the performance of the examples and comparative examples in Table 1, all examples are generally superior to the comparative example in key indicators such as viscosity, low-temperature stability, water-insoluble content, and zinc-iron encapsulation rate. The viscosity of Examples 1-4 at 25℃ was controlled within the range of 95-140 mPa·s, and no crystallization or significant stratification occurred after standing at -5℃ for 7 days. This indicates that the appropriate content (1.5-4.5 wt%) of core-shell nanocomposite intermediate A and the optimized nutrient ratio effectively resolved the contradiction between low viscosity and stability in a high ionic strength system. Comparative Example 1, due to the excessively low content of intermediate A (0.3 wt%), resulted in a zinc-iron encapsulation rate of only 35%, and D... 50 The particle size increased to 120 nm, the PDI increased to 0.28, and the absolute value of the Zeta potential decreased to 18 mV, resulting in slight stratification. Comparative Example 2 had a significantly increased viscosity (245 mPa·s), excessive water-insoluble matter (0.32 wt%), and an increased PDI (0.32) with obvious stratification due to excessive intermediate A content (5.5 wt%). Although the zinc-iron encapsulation rate reached 78%, the overall processing compatibility was severely deteriorated. Comparative Examples 3-4 had low-temperature crystallization due to nutrient imbalance or improper ammonium-nitrate ratio. The total nitrogen in Comparative Example 3 was too low (13.0 wt%), causing the conductivity to drop to 18.0 mS / cm due to insufficient nutrient concentration. The ammonium-nitrate ratio in Comparative Example 4 was severely imbalanced (10:90), resulting in a large amount of nitrate crystallization at low temperature. Comparative Example 6 had an incomplete core structure due to insufficient polyγ-glutamic acid (3 parts by mass) during the preparation of prepolymer P, resulting in a zinc-iron encapsulation rate of 42% and D 50 The particle size increased to 145 nm, the PDI increased to 0.35, and the absolute value of the Zeta potential decreased to 16 mV, while exhibiting both crystallization and significant stratification failure. Comparative Example 7, due to the lack of high-shear dispersion and ultrasonic treatment, resulted in severe nanoparticle agglomeration. 50The particle size surged to 280 nm, the PDI deteriorated to 0.52, the absolute value of the Zeta potential decreased to 12 mV, the zinc-iron encapsulation rate decreased to 38%, and the water-insoluble matter increased to 0.28 wt% with obvious sedimentation and stratification, fully demonstrating the key role of high-shear ultrasonication in constructing a highly dispersed and stable core-shell structure. In Comparative Example 8, insufficient fulvic acid (3 parts by mass) during the preparation of intermediate A resulted in inadequate shell coating, with the zinc-iron encapsulation rate decreasing to 48%. 50 The increase in particle size to 130 nm, the rise in PDI to 0.29, and the decrease in absolute value of Zeta potential to 19 mV indicate the importance of fulvic acid dosage for shell integrity and trace element immobilization efficiency. In summary, the technical solution of this invention achieves the organic unity of low viscosity pumpability (95-140 mPa·s at 25℃), wide temperature range storage stability (no crystallization or stratification at -5℃ to 40℃), and stable immobilized slow release of zinc and iron trace elements (encapsulation rate 50-90%, preferably 70-90%) through precise control of core-shell nanocomposite intermediate A (0.5-5.0 wt%, preferably 1.5-4.5 wt%), optimization of ammonium-nitrate ratio (20-80:80-20, preferably 40:60 to 60:40), synergistic design of ammonium polyphosphate-polyγ-glutamic acid prepolymer (mass ratio 100:3-20, preferably 100:8-16), and high shear ultrasonic dispersion process (3000-6000 rpm + 20-40 kHz) of high-nutrient water-soluble fertilizer (total nutrients ≥40 wt%), and nanoparticles D. 50 Controlling the concentration to 50-150nm with PDI≤0.25 and absolute Zeta potential≥20mV ensures long-term dispersion stability. Water-insoluble matter≤0.2wt% meets the filtration requirements of drip irrigation systems, fundamentally solving the multiple technical bottlenecks of existing high-concentration water-soluble fertilizers that are difficult to balance processing adaptability, clarification stability and preservation of effective forms of trace elements under high ionic strength and high solid content formulation conditions.

[0168] Table 1 Performance summary of examples and comparative examples

[0169]

[0170] 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 water-soluble fertilizer for stress resistance and yield increase in winter wheat, characterized in that, The aforementioned water-soluble fertilizer for winter wheat stress resistance and yield enhancement is an aqueous solution using deionized water as a solvent, comprising the following components, based on the total mass of the finished product: (1) The total nitrogen is 15–22 wt%, which is provided by urea, ammonium nitrate, and ammonium polyphosphate, and optionally also includes potassium nitrate to provide nitrate nitrogen, and the mass ratio of ammonium nitrogen to nitrate nitrogen is 20–80:80–20, wherein the mass ratio of ammonium nitrogen to nitrate nitrogen is calculated based on the nitrogen provided by nitrogen-containing salts other than urea, the ammonium nitrogen includes the ammonium nitrogen provided by ammonium nitrate and ammonium polyphosphate, the nitrate nitrogen includes the nitrate nitrogen provided by ammonium nitrate and, if present, potassium nitrate, and the nitrogen provided by urea is not included in the calculation of the mass ratio of ammonium nitrogen to nitrate nitrogen; (2) The total phosphorus nutrient content, converted to phosphorus pentoxide, is 5–12 wt%, which is provided by ammonium polyphosphate; (3) The total potassium nutrient content, converted to potassium oxide, is 8–18 wt%, provided by at least one of potassium nitrate and potassium sulfate; (4) 0.5–5.0 wt% of solids containing core-shell nanocomposite intermediate A, wherein core-shell nanocomposite intermediate A is formed by the reaction of ammonium polyphosphate, polyγ-glutamic acid, fulvic acid, zinc sulfate heptahydrate and ferrous sulfate heptahydrate in an aqueous phase; (5) Contains 0.1–1.0 wt% free fulvic acid, wherein the free fulvic acid is fulvic acid added in addition to the fulvic acid contained in the core-shell nanocomposite intermediate A; (6) Contains magnesium sulfate heptahydrate, with a medium element nutrient content of 0.5–3.0 wt% when converted to magnesium oxide; (7) Contains 0.1–0.8 wt% of trisodium citrate dihydrate, wherein the trisodium citrate dihydrate is used as a complexing agent; (8) The total zinc content in the finished product is 0.02–0.20 wt%, and the total iron content is 0.02–0.20 wt%, wherein zinc and iron are at least partially present in the shell form of the core-shell nanocomposite intermediate A, and optionally also in the free form of at least one of zinc sulfate heptahydrate and ferrous sulfate heptahydrate; (9) The remainder is deionized water and unavoidable impurities.

2. The water-soluble fertilizer for stress resistance and yield increase of winter wheat as described in claim 1, characterized in that, The nitrogen provided by urea accounts for 20–60 wt% of the total nitrogen, and the nitrogen provided by potassium nitrate accounts for 0–30 wt% of the total nitrogen.

3. The water-soluble fertilizer for stress resistance and yield increase of winter wheat as described in claim 1, characterized in that, The core of the core-shell nanocomposite intermediate A in the water-soluble fertilizer for stress resistance and yield increase of winter wheat is prepolymer P. The prepolymer P is a prepolymer formed by ammonium polyphosphate and polyγ-glutamic acid. The prepolymer P is prepared by a method including the following steps: A1. Dissolve 100–150 parts by mass of ammonium polyphosphate in deionized water at 50–70℃ to obtain a homogeneous solution. Slowly add 3–20 parts by mass of polyγ-glutamic acid at 60–80℃ with continuous stirring to make the mass ratio of ammonium polyphosphate to polyγ-glutamic acid 100:3–20. Continue stirring for 1–3 hours. A2. Adjust the pH of the reaction solution to 5.5–6.5 using sodium hydroxide or hydrochloric acid; A3. Concentrate the reaction solution under reduced pressure at 50–70°C to a solids mass fraction of 30–45 wt%. A4. When the viscosity of the prepolymer solution at 25°C is 500–3000 mPa·s, and the pH value changes by no more than 0.2 within 30 minutes under constant temperature conditions at 25°C, the concentration is stopped, the solution is cooled, and insoluble matter is removed by passing it through a 100-mesh filter to obtain the prepolymer P.

4. The water-soluble fertilizer for stress resistance and yield increase of winter wheat as described in claim 1, characterized in that, The preparation of the core-shell nanocomposite intermediate A includes the following steps: B1. Take prepolymer P, dilute it with deionized water to a solids mass fraction of 10–25 wt%, and stir at 35–45 °C; B2. Based on the solids of prepolymer P, add 5–40 parts by mass of fulvic acid to the solution obtained in step B1 based on 100 parts by mass of prepolymer P, and stir at 35–45°C for 0.5–1.5 h. B3. Prepare a metal salt solution by dissolving zinc sulfate heptahydrate and ferrous sulfate heptahydrate in deionized water, controlling the molar ratio of zinc to iron to be 0.5–3:

1. Add the metal salt solution dropwise to the system in step B2 at 35–55°C, while simultaneously adding trisodium citrate dihydrate to make the molar ratio of trisodium citrate dihydrate to the total amount of zinc and iron 0.1–0.5:

1. Adjust the pH value to 5.0–6.5 using sodium hydroxide or hydrochloric acid, and continue stirring for 1–3 hours. B4. After step B3, apply high shear dispersion at 3000–6000 rpm to the reaction solution for 10–30 min, and then perform ultrasonic treatment at a frequency of 20–40 kHz and a sound power density of 0.5–1.5 W / cm² for 5–15 min. B5. Large particles or gels are removed by filtration through a filter cartridge with a pore size of 1–5 μm to obtain a dispersion of core-shell nanocomposite intermediate A, wherein the nanoparticles in the dispersion have a D 50 The nanoparticles have a size of 50–150 nm, a PDI of no more than 0.25, and contain 5–15 wt% zinc and iron in their shells on a dry basis. The pH value is 5.0–6.5, and no visible precipitate is observed after standing for 24 hours.

5. The water-soluble fertilizer for stress resistance and yield increase of winter wheat as described in claim 1, characterized in that, The viscosity of the water-soluble fertilizer was measured using a rotational viscometer. The viscosity measured at any temperature within the temperature range of −5℃ to 40℃ was no higher than 300 mPa·s. After standing at −5℃ for 7 days, there was no crystallization or obvious stratification. The conductivity of the solution prepared at 25℃ with a mass fraction of 10wt% was 15–40 mS / cm. The viscosity at 25°C is not higher than 150 mPa·s; No visible crystallization occurred when the mixture was left to stand in a sealed container at 0°C for 7 days. The content of water-insoluble matter is not higher than 0.2 wt%; The pH value is 5.5–7.

0.

6. A method for preparing the water-soluble fertilizer for stress resistance and yield increase of winter wheat according to any one of claims 1-5, characterized in that, The method includes the following steps: S1. Add deionized water to the reaction vessel, wherein the amount of deionized water added is 10-30 wt% of the total mass of the finished product. At 30-60°C, add at least one of ammonium polyphosphate, urea, ammonium nitrate, potassium nitrate and potassium sulfate, as well as magnesium sulfate heptahydrate, in sequence. Stir for 30-60 min until completely dissolved, and the solution is clear to the naked eye and free of visible solid particles as the criterion. S2. When the reaction solution temperature is 25–45℃, add a dispersion of core-shell nanocomposite intermediate A, wherein the solid mass fraction of the dispersion of core-shell nanocomposite intermediate A is 5–25 wt%, and the amount of the dispersion of core-shell nanocomposite intermediate A added is 2–40 wt% of the total mass of the finished product, so that the solid mass fraction of the core-shell nanocomposite intermediate A in the finished product is 0.5–5.0 wt%, and maintain a shear speed of 1000–3000 rpm for stirring for 10–30 min; S3. At 20–40℃, add free fulvic acid and trisodium citrate dihydrate, continue stirring for 20–40 min, and adjust the pH to 5.5–7.0 with a sodium hydroxide solution of 10–40 wt% or a hydrochloric acid solution of 10–37 wt%. S4. Cool the mixed solution obtained in step S3 to no higher than 30°C, filter it through a filter element with a pore size of 5–20 μm to remove water-insoluble matter, and fill and seal it under the condition that the water-insoluble matter content is no higher than 0.2 wt% to obtain the winter wheat stress-resistant and yield-increasing water-soluble fertilizer.

7. The preparation method according to claim 6, characterized in that, In step S1, the feeding order of at least one of ammonium polyphosphate, urea, ammonium nitrate, potassium nitrate and potassium sulfate, and magnesium sulfate heptahydrate is ammonium polyphosphate, urea, ammonium nitrate, potassium nitrate and potassium sulfate, and magnesium sulfate heptahydrate.

8. The preparation method according to claim 6, characterized in that, In step S2, the shearing and stirring speed is 1500–2500 rpm, the shearing time is 15–25 min, and an ultrasonic field is applied during the shearing and stirring process. The frequency of the ultrasonic field is 20–40 kHz, the sound power density is 0.5–1.5 W / cm², and the ultrasonic time is 5–15 min.

9. The preparation method according to claim 6, characterized in that, In step S3, the amount of free fulvic acid added is controlled so that the mass fraction of fulvic acid in the finished product is 0.2–0.8 wt%, and the amount of trisodium citrate dihydrate added is controlled so that the mass fraction of trisodium citrate dihydrate in the finished product is 0.1–0.5 wt%.

10. The preparation method according to claim 6, characterized in that, In step S4, the solution is cooled and aged at 0–5℃ for 2–24 hours before filtration to remove potential crystal nuclei, thereby improving the low-temperature storage stability of the finished product. The preparation method is a continuous production process. Steps S1–S4 are connected by an online metering pump, a static mixer, and an online pH and conductivity detection unit. The batch-to-batch deviation of the mass fraction of total nitrogen, total phosphorus, and total potassium in each batch of finished product is controlled to be no more than ±5%. The water-soluble fertilizer for winter wheat stress resistance and yield increase obtained by the preparation method is subjected to temperature cycling treatment of −5–40℃. One cycle consists of holding at −5℃ for 24 hours and holding at 40℃ for 24 hours. After a total of 3 cycles, the water-insoluble matter content increases by no more than 0.1 mass fraction points.

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