Drought-resistant foliar fertilizer containing nano-zinc oxide for soybean planting and preparation method thereof

Abstract

This invention relates to the field of organic fertilizer manufacturing technology, specifically to a drought-resistant foliar fertilizer containing nano-zinc oxide for soybean cultivation and its preparation method. This invention overcomes the problems of rapid nutrient loss, low absorption efficiency, and easy cell damage in soybeans under drought stress. The raw materials for this invention include enzymatically hydrolyzed alginic acid, compound amino acids, sugar alcohol complexing agents, tea polyphenols, and a fulvic acid-tea polyphenol dual-modified carrier. By loading nano-zinc oxide inside a silica carrier and utilizing the interface dual cross-linking modification of tea polyphenols and fulvic acid, a "smart-gated" release system sensitive to water and osmotic pressure is constructed. Combined with the endogenous osmotic regulation of enzymatically hydrolyzed alginic oligosaccharides and L-proline, and the bio-interface adhesion and UV-resistant antioxidant properties of tea polyphenols, the drought resistance and water retention capacity of soybeans and the pod-setting rate can be significantly improved.

Description

Technical Field

[0001] This invention relates to the field of organic fertilizer manufacturing technology, specifically to a drought-resistant foliar fertilizer containing nano-zinc oxide for soybean cultivation and its preparation method. Background Technology

[0002] Soybeans are an important grain and oil crop in my country. During the soybean growth cycle, especially the flowering and pod-setting stage, the demand for water is extremely high. However, in recent years, due to the impact of global climate change, drought stress has become frequent, leading to abnormal closure of stomata in soybean leaves, decreased photosynthesis, and severe flower and pod drop, ultimately resulting in significant yield reductions. Organic foliar fertilizers, as a fast-acting nutrient supplement, play an important role in alleviating drought stress in crops.

[0003] Zinc is an essential micronutrient for soybean growth, promoting auxin synthesis and participating in regulating the level of endogenous hormones in plants under drought conditions, thereby enhancing drought resistance. In recent years, nano-zinc oxide has attracted much attention due to its large specific surface area and strong permeability. However, existing foliar fertilizers containing nano-zinc oxide are mostly simple mixtures of inorganic salts or organic matter, which have two core problems: First, the release rate of traditional nano-zinc fertilizers is fixed after foliar spraying and cannot be dynamically adjusted according to changes in the leaf surface microenvironment (such as osmotic pressure and pH value) caused by drought, resulting in "excess before drought and deficiency during drought"; Second, soybean leaves are densely covered with villi, and drought is often accompanied by strong ultraviolet radiation and hot, dry winds. Ordinary foliar fertilizer droplets have difficulty penetrating the villi layer to reach the epidermal cells, and they rapidly lose water and crystallize at high temperatures. Organic active ingredients are easily degraded and inactivated under strong ultraviolet radiation, resulting in an extremely short fertilizer effect window.

[0004] Therefore, developing an organic-inorganic hybrid foliar fertilizer that can intelligently release nutrients in response to water stress, resist ultraviolet radiation, and strongly adhere to the surface of hairy leaves is of great significance for improving the stress resistance and stable yield of soybeans in my country.

[0005] To this end, a drought-resistant foliar fertilizer containing nano-zinc oxide for soybean cultivation and its preparation method are proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a drought-resistant foliar fertilizer containing nano-zinc oxide for soybean cultivation and its preparation method, in order to solve the problems of rapid nutrient loss, low absorption efficiency, and easy cell damage in soybeans under drought stress. The raw materials for preparation include enzymatically hydrolyzed alginic acid, compound amino acids, sugar alcohol complexing agents, tea polyphenols, and a fulvic acid-tea polyphenol dual-modified carrier. By loading nano-zinc oxide inside a silica carrier and utilizing the interface dual cross-linking modification of tea polyphenols and fulvic acid, a "smart-gated" release system sensitive to water and osmotic pressure is constructed. Combined with the endogenous osmotic regulation of enzymatically hydrolyzed alginic oligosaccharides and L-proline, and the bio-interface adhesion and UV-resistant antioxidant properties of tea polyphenols, the drought resistance and water retention capacity of soybeans and the pod-setting rate can be significantly improved.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] Unless otherwise specified, all parts in this invention are parts by weight.

[0009] This invention provides a method for preparing a drought-resistant foliar fertilizer containing nano-zinc oxide for soybean cultivation. The preparation method is as follows: 60 parts of deionized water are added to a reaction vessel and heated to 50°C. Then, 12-20 parts of enzymatically hydrolyzed alginic acid, 6-13 parts of compound amino acids, 6 parts of sugar alcohol complexing agent, and 1.5-3.5 parts of tea polyphenols (EGCG content ≥50%, total polyphenols ≥98%) are added sequentially. The mixture is stirred at 800 rpm for 1 hour to ensure complete hydration of the macromolecules. Finally, 8-15 parts of fulvic acid are added... A tea polyphenol dual-modified carrier was used. A high-shear emulsifier was started, and the speed was adjusted to 4000-5500 rpm. Under the temperature control of the external jacket cooling water, the system temperature was maintained at 40℃ for shear dispersion for 10 minutes. This step enabled the polyphenol layer on the carrier surface and the alginate molecular chain to achieve microscopic interpenetration through hydrogen bonds and van der Waals forces. One part of organosilicon surfactant was added, the speed was reduced to 150 rpm, and the temperature was lowered to 25℃ for static curing for 24 hours. This allowed the chemical bonding inside the system to reach dynamic equilibrium, resulting in a drought-resistant foliar fertilizer.

[0010] The long-term maturation process at 25℃ avoids the damage of high temperature to the gating activity of fulvic acid-tea polyphenol complex, and retains the gating's ultra-sensitive response to water molecules. This allows the foliar fertilizer to accurately capture physiological signals in the early stages of drought and activate nutrient supply mode after entering the soybean leaves.

[0011] Preferably, the compound amino acid is plant-derived hydrolyzed amino acid powder.

[0012] Preferably, the sugar alcohol complexing agent is obtained by compounding xylitol and sorbitol in a mass ratio of 1:1.

[0013] The preferred method for preparing the fulvic acid-tea polyphenol dual-modified carrier is as follows: The aminated carrier is added to 200 mL of a 5% (w / w) aqueous solution of tea polyphenols, and 0.1%-0.8% (w / w) of ferric chloride is added as a crosslinking accelerator. The mixture is reacted at 400 rpm and 35°C for 3 h. Then, 180 mL of a 10% (w / w) aqueous solution of potassium fulvicate (pH adjusted to 8.5 with 10% KOH solution) is added, and the reaction continues for 2.4-3.2 h. The mixture is filtered, washed three times with deionized water to remove free impurities, dried in a vacuum drying oven at 55°C for 12 h, and pulverized through a 200-mesh sieve to obtain the fulvic acid-tea polyphenol dual-modified carrier.

[0014] Preferably, the preparation method of the amination carrier is as follows: 50g of porous silica (pore size 200nm) is added to 500mL of 15% (w / w) nano-zinc oxide (nearly spherical, average particle size 30nm) ethanol dispersion, placed in a vacuum drying oven, and evacuated to below -0.08MPa for 30min (to remove air from the pores). Then, it is slowly restored to normal pressure and ultrasonically dispersed for 15min (using atmospheric pressure to force droplets into deep pores, and the "cavitation effect" generated by ultrasound can further disperse any possible blockages). After repeating the vacuum-normal pressure-ultrasonic operation three times, the particles agglomerate at the orifice were centrifuged and washed with ethanol to remove free nano-zinc oxide that did not enter the pores or was weakly attached. The zinc-loaded powder was then dried. The zinc-loaded powder was dispersed in 450 mL of 95% ethanol aqueous solution, and silane coupling agent KH-550 was added at a mass ratio of 1:0.05. The mixture was refluxed at 600 rpm and 65-80℃ for 4 h to obtain an aminated support.

[0015] The preferred method for preparing alginic acid by enzymatic hydrolysis is as follows: Add *Alternaria buergeriana* powder to deionized water at a solid-liquid ratio of 1:12, stir at 400 rpm, heat to 55°C, and maintain for 2 hours to allow the algae polysaccharides to fully swell and release the encapsulated minerals; adjust the pH to 7.0 using sodium bicarbonate, add a compound enzyme at 1.5% of the raw material mass, and hydrolyze at 40°C and 300 rpm for 6 hours. When the system viscosity drops below 20 mPa·s, it indicates that the large-molecule alginic acid has been degraded into more active small-molecule oligosaccharides. Add 2% of the raw material mass... 3% citric acid monohydrate was heated to 80℃ and stirred at 500 rpm for 1-2 hours. During this process, one carboxyl group of citric acid formed a hydrogen bond complex with the hydroxyl group on the seaweed oligosaccharide, and the remaining carboxyl group was exposed on the outside of the molecular chain. After the reaction, impurities were filtered through a 200-mesh filter, and the filtrate was concentrated through a vacuum membrane to a solid content of 30% to obtain enzymatically hydrolyzed alginate. The complex enzyme was obtained by mixing alginate lyase (20000 U / g) and cellulase (50000 U / g) at a mass ratio of 2.5-3.5:1.

[0016] The preferred method for preparing plant-derived hydrolyzed amino acid powder is as follows: Take 100g of defatted soybean flour as raw material, add deionized water at a solid-liquid ratio of 1:8, stir and disperse at 500rpm, and use 5% Adjust the pH to 8.0 with NaOH solution, add 1.2% (by weight of raw material) of neutral protease (enzyme activity ≥100000U / g), and hydrolyze at 50℃ for 4 hours. Then, raise the temperature to 55℃ and use 10wt% citric acid solution to adjust the pH back to 6.0. Add 0.5% (by weight of raw material) of flavor enzyme (enzyme activity ≥50000U / g) for deep hydrolysis for 3 hours. Inactivate the enzyme by raising the temperature to 95℃ and holding for 15 minutes. After cooling to room temperature, centrifuge at 5000rpm for 20 minutes to remove residue. Collect the supernatant and concentrate it to a solid content of 50%. Based on the final product dry weight, add L-proline powder (specific rotation -84.3° to -86.0°) to the concentrate to achieve a L-proline content of 45% in the total amino acids. Perform instantaneous drying using a pressure spray drying tower with an inlet air temperature of 170℃ and an outlet air temperature of 85℃ to obtain plant-derived hydrolyzed amino acid powder.

[0017] Another aspect of the present invention provides a drought-resistant foliar fertilizer containing nano zinc oxide for soybean cultivation. The drought-resistant foliar fertilizer is prepared by any of the above preparation methods. The raw materials for preparing the drought-resistant foliar fertilizer include humic acid-tea polyphenol dual-modified carrier, enzymatically hydrolyzed alginic acid, compound amino acids, sugar alcohol complexing agent, tea polyphenols and organosilicon surfactant.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] 1. This invention constructs an environmentally responsive "gated" structure through the layer-by-layer self-assembly of an aminated carrier with tea polyphenols and potassium humate. In-situ oxidative cross-linking of tea polyphenols and iron ions forms the first bioadhesive membrane on the carrier surface. Secondary gating is then achieved through humic acid. Under sufficient moisture conditions, the polymer chains are fully hydrated and swollen, sealing the pores and locking in the internal nano-zinc oxide. When soybeans experience drought stress and the osmotic pressure of the leaf microenvironment increases, the polymer layer dehydrates due to the osmotic pressure difference, causing the composite gated conformation to shrink and curl, opening the pores and actively releasing zinc ions. This synergistic mechanism of "drought-triggered, on-demand release" overcomes the drawbacks of uncontrollable release from traditional foliar fertilizers, ensuring that nutrients exert maximum effectiveness during the window of opportunity when the plant most needs drought resistance regulation.

[0020] 2. To address the problem of fertilizer application and detachment caused by the abundant hairs and thick waxy coating on soybean leaves, this invention introduces tea polyphenols with superior interfacial activity for modification. The abundant catechol groups in the tea polyphenol structure possess strong interfacial adhesion properties. Combined with the physical film-forming properties of enzymatically hydrolyzed alginic acid, it can form strong multi-point hydrogen bond adsorption and covalent bonding with the cuticle and villi of soybean leaves. This allows a highly resilient microscopic film to quickly form after foliar fertilizer application, maintaining a firm bond even in severe weather conditions such as drought accompanied by strong winds or occasional showers, significantly extending the effective absorption time.

[0021] 3. This invention achieves a deep physiological synergy of "organic induction + inorganic regulation" in its formulation. The specially formulated small-molecule enzymatically hydrolyzed seaweed oligosaccharide has extremely strong penetrating power. After entering the mesophyll cells, it acts as an inducer to first activate the expression of endogenous stress-resistance genes in soybeans. Simultaneously released nano-zinc oxide rapidly catalyzes the synthesis of related drought-resistant enzyme systems. The high content of L-proline is used as an excellent osmotic pressure protectant to maintain cell turgor pressure. The three interact synergistically to form a three-dimensional drought-resistant network from gene signal warning to physiological osmotic regulation, which greatly enhances the ability of soybeans to resist water shortage and retain pods during the flowering and pod-setting stages.

[0022] 4. Drought is often accompanied by high temperatures and strong radiation, which can easily trigger an explosion of reactive oxygen species and photo-oxidative damage in leaves. This application utilizes a dual-modified coating of fulvic acid and tea polyphenols to construct an anti-ultraviolet shielding layer on the surface of foliar fertilizer. This composite modified layer not only efficiently absorbs and shields ultraviolet rays, preventing the degradation and damage of free amino acids and alginic acid by strong light, but also exerts a strong antioxidant effect, effectively quenching / scavenging free radicals. During drought, the system can rapidly neutralize harmful reactive oxygen species produced by damaged mesophyll cells, maintain the lipid integrity of cell membranes, effectively delay leaf yellowing and premature aging caused by drought, and ensure the continuous operation of photosynthesis.

[0023] 5. Addressing the process pain point of flocculation and sedimentation when organic macromolecules are combined with inorganic nanomaterials, this invention employs in-situ esterification and high-shear micro-intercalation technology. After citric acid esterification modification, seaweed oligosaccharides expose a large number of activated carboxyl groups. Driven by specific shear forces, these carboxyl groups undergo strong hydrogen bonding crosslinking and electrostatic anchoring with the polyphenol coordination layer and residual amino groups on the modified carrier surface. This transforms alginate from a substance encapsulated outside the carrier into part of the carrier itself. This combination of material modification and process parameters constructs a highly stable "suspended microgel interpenetrating network" in the liquid phase, effectively avoiding stratification during long-term storage and enhancing the industrial application value of the product. Attached Figure Description

[0024] Figure 1 The graph shows the test results of the zinc release rate in response to moisture in Examples 1-4 of this invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Please see Figure 1 This invention provides a drought-resistant foliar fertilizer containing nano-zinc oxide for soybean cultivation and its preparation method. The technical solution is as follows:

[0027] Example 1

[0028] 50g of porous silica (pore size 200nm) was added to 500mL of a 15% (w / w) ethanol dispersion of nano-zinc oxide (nearly spherical, average particle size 30nm). The mixture was placed in a vacuum drying oven, heated to 45℃, and evacuated to below -0.08MPa for 30min. Then, the vent valve of the vacuum oven was slowly opened to allow outside air to enter the oven. The pressure was allowed to rise back to normal pressure over 1min. The system was then placed in an ultrasonic cleaner (300W, 40kHz) preheated to 45℃ for 15min. This vacuum-to-normal-pressure-ultrasonic process was repeated three times. The mixture was then kept at 450rpm and 45℃ for 24h, centrifuged, washed with ethanol, and dried at 60℃ for 12h to obtain zinc-loaded powder. All the zinc-loaded powder was dispersed in 450mL of... A silane coupling agent, KH-550, was added to a 95% ethanol aqueous solution at a mass ratio of 1:0.05. The mixture was refluxed at 600 rpm and 65°C for 4 hours to obtain an aminated carrier. The aminated carrier was then added to 200 mL of a 5% (w / w) tea polyphenol aqueous solution (tea polyphenol EGCG content ≥50%, total polyphenols ≥98%). 0.1% (w / w) of ferric chloride was added as a crosslinking promoter, and the mixture was reacted at 400 rpm and 35°C for 3 hours. 180 mL of a 10% (w / w) potassium humate aqueous solution (pH adjusted to 8.5 with 10% KOH solution) was added, and the reaction continued for 2.4 hours. The mixture was filtered, washed three times with deionized water, dried in a vacuum drying oven at 55°C for 12 hours, and pulverized through a 200-mesh sieve to obtain a humic acid-tea polyphenol dual-modified carrier.

[0029] 100g of *Alternaria lobata* powder was added to deionized water at a solid-liquid ratio of 1:12. The mixture was stirred at 400 rpm and heated to 55℃ for 2 hours. The pH was adjusted to 7.0 using sodium bicarbonate. A compound enzyme at 1.5% of the raw material mass was added, and the mixture was hydrolyzed at 40℃ and 300 rpm for 6 hours. When the viscosity of the system dropped below 20 mPa·s, 2% of the raw material mass of citric acid monohydrate was added. The mixture was heated to 80℃ and stirred at 500 rpm for 1 hour. Impurities were filtered through a 200-mesh filter, and the filtrate was concentrated through a vacuum membrane to a solid content of 30% to obtain enzymatically hydrolyzed alginic acid. The compound enzyme was obtained by mixing alginic acid lyase (20000 U / g) and cellulase (50000 U / g) at a mass ratio of 2.5:1.

[0030] Add 60 parts of deionized water to the reactor and heat to 50℃. Then add 12 parts of enzymatically hydrolyzed alginic acid, 6 parts of compound amino acids, 6 parts of sugar alcohol complexing agent, and 1.5 parts of tea polyphenols (EGCG content ≥50%, total polyphenols ≥98%) in sequence. Stir at 800 rpm for 1 hour. Add 8 parts of fulvic acid-tea polyphenol dual-modified carrier, start the high-shear emulsifier, adjust the speed to 4000 rpm, and maintain the system temperature at 40℃ for shear dispersion for 10 minutes under external jacket cooling water temperature control. Add 1 part of organosilicon surfactant Silwet L-77, reduce the speed to 150 rpm, cool to 25℃ and let stand for 24 hours to mature, thus obtaining drought-resistant foliar fertilizer. The compound amino acids are plant-derived hydrolyzed amino acid powder, of which L-proline content is 45%. The sugar alcohol complexing agent is obtained by compounding xylitol and sorbitol in a 1:1 mass ratio.

[0031] The preparation method of compound amino acids is as follows: Take 100g of defatted soybean flour as raw material, add deionized water at a solid-liquid ratio of 1:8, stir and disperse at 500rpm, and use 5% Adjust the pH to 8.0 with NaOH solution, add 1.2% (by weight of raw material) of neutral protease (enzyme activity ≥100000U / g), and hydrolyze at 50℃ for 4 hours. Then, raise the temperature to 55℃ and use 10wt% citric acid solution to adjust the pH back to 6.0. Add 0.5% (by weight of raw material) of flavor enzyme (enzyme activity ≥50000U / g) for deep hydrolysis for 3 hours. Inactivate the enzyme by raising the temperature to 95℃ and holding for 15 minutes. After cooling to room temperature, centrifuge at 5000rpm for 20 minutes to remove residue. Collect the supernatant and concentrate it to a solid content of 50%. Based on the final product dry weight, add L-proline powder (specific rotation -84.3° to -86.0°) to the concentrate to achieve a L-proline content of 45% in the total amino acids. Perform instantaneous drying using a pressure spray drying tower with an inlet air temperature of 170℃ and an outlet air temperature of 85℃ to obtain a pale yellow plant-derived hydrolyzed amino acid powder, i.e., complex amino acids.

[0032] Example 2

[0033] Referring to the preparation method and parameters of Example 1, the differences are as follows: when preparing the fulvic acid-tea polyphenol dual-modified carrier, the KH-550 reflux temperature was 75℃, the amount of ferric chloride was 0.5%, and the reaction was carried out for 2.8h after adding potassium fulvic acid; when preparing the enzymatic hydrolysis of alginic acid, the mass ratio of the compound enzyme was 3:1, the amount of citric acid was 2.5%, and the reaction was carried out at 80℃ for 1.5h; when preparing the foliar fertilizer, 16 parts of enzymatically hydrolyzed alginic acid, 10 parts of compound amino acids, 2.5 parts of tea polyphenols, and 12 parts of fulvic acid-tea polyphenol dual-modified carrier were added, and the shearing speed was 4800rpm.

[0034] Example 3

[0035] Referring to the preparation method and parameters of Example 1, the differences are as follows: when preparing the fulvic acid-tea polyphenol dual-modified carrier, the KH-550 reflux temperature was 80℃, the amount of ferric chloride was 0.8%, and the reaction was carried out for 3.2 hours after adding potassium fulvic acid; when preparing the enzymatic hydrolysis of alginic acid, the mass ratio of the compound enzyme was 3.5:1, the amount of citric acid was 3%, and the reaction was carried out at 80℃ for 2 hours; when preparing the foliar fertilizer, 20 parts of enzymatically hydrolyzed alginic acid, 13 parts of compound amino acids, 3.5 parts of tea polyphenols, and 15 parts of fulvic acid-tea polyphenol dual-modified carrier were added, and the shearing speed was 5500 rpm.

[0036] Example 4

[0037] Referring to the preparation method and parameters of Example 1, the differences are as follows: when preparing the fulvic acid-tea polyphenol dual-modified carrier, the KH-550 reflux temperature was 70℃, the amount of ferric chloride was 0.3%, and the reaction was carried out for 3 hours after adding potassium fulvic acid; when preparing the enzymatic hydrolysis of alginic acid, the mass ratio of the compound enzyme was 2.8:1, the amount of citric acid was 2.8%, and the reaction was carried out at 80℃ for 1.8 hours; when preparing the foliar fertilizer, 18 parts of enzymatically hydrolyzed alginic acid, 8 parts of compound amino acids, 2 parts of tea polyphenols, and 10 parts of fulvic acid-tea polyphenol dual-modified carrier were added, and the shearing speed was 5000 rpm.

[0038] Comparative Example 1

[0039] The preparation method and parameters of Example 1 are the same, except that in the foliar fertilizer formulation stage, instead of adding the fulvic acid-tea polyphenol dual-modified carrier, an equivalent amount (with the same zinc content after conversion) of unmodified ordinary nano zinc oxide powder is directly added.

[0040] Comparative Example 2

[0041] The preparation method and parameters of Example 1 are the same, except that when preparing the dual-modified carrier, the aminated carrier is reacted directly with potassium humate without adding tea polyphenol aqueous solution and ferric chloride, in order to prepare a single-layer humic acid modified carrier.

[0042] Comparative Example 3

[0043] The preparation method and parameters of Example 1 are the same, except that when preparing the fulvic acid-tea polyphenol dual-modified carrier, the aminated carrier reacts only with tea polyphenols and ferric chloride, without adding potassium fulvic acid solution, to prepare a single-layer tea polyphenol modified carrier.

[0044] Comparative Example 4

[0045] The preparation method and parameters of Example 1 are the same, except that the step of adding KH-550 for reflux amination is omitted during the preparation of the carrier. Instead, the zinc-loaded powder is directly added to the tea polyphenol solution for subsequent encapsulation (physical adsorption instead of chemical grafting).

[0046] Comparative Example 5

[0047] The preparation method and parameters of Example 1 are the same, except that in the preparation stage of alginate, the step of adding a compound enzyme for hydrolysis is omitted, and the macromolecular bubbly algae stock solution is directly treated with citric acid.

[0048] Comparative Example 6

[0049] The preparation method and parameters of Example 1 are the same, except that in the final stage of the preparation of alginate by enzymatic hydrolysis, citric acid monohydrate is not added for heating reaction, and the enzymatic hydrolysate is directly concentrated for use.

[0050] Comparative Example 7

[0051] The preparation method and parameters are the same as in Example 1, except that tea polyphenols are not added in the liquid phase miscibility stage of the foliar fertilizer preparation step.

[0052] Comparative Example 8

[0053] The preparation method and parameters of Example 1 are the same, except that when adding the fulvic acid-tea polyphenol dual-modified carrier to the system, a high-shear emulsifier is not used, but conventional mechanical stirring at 800 rpm for 20 min is used instead.

[0054] Experiment Example 1 Performance Testing

[0055] Leaf scour resistance retention rate (characterizing adhesion): An equal volume of diluted solution (500 times dilution) was evenly sprayed on the leaves of potted soybeans. After natural drying for 24 hours, moderate rainfall (15 mm / h, lasting 1 hour) was applied using an artificial rainfall simulator. The leaves were collected, and the residual zinc content was determined by atomic absorption spectrometry (AAS) to calculate the retention rate.

[0056] Water-responsive zinc release rate (characterizing intelligent slow release): Using the dynamic dialysis bag method, equal amounts of fertilizer were placed into dialysis bags. Each dialysis bag (molecular weight cutoff 8000-14000 Da) contained 5.0 mL of fertilizer stock solution and was placed in deionized water (simulating sufficient water, osmotic pressure 0 MPa) and 20% PEG-6000 solution (simulating severe drought stress, osmotic pressure approximately -1.0 MPa), respectively. After 24 h, the zinc ion release rate of the external solution was measured.

[0057] Malondialdehyde (MDA) content (characterizing drought resistance and physiological protection): Potted soybeans were subjected to continuous drought treatment for 7 days during the flowering period (a diluted solution was sprayed once on the 3rd day of the drought treatment); soybean leaves were sampled, and the MDA content was determined by the thiobarbituric acid (TBA) colorimetric method. The lower the MDA content, the less damage the cell membrane is caused by reactive oxygen species oxidation, and the better the drought resistance protection.

[0058] Centrifugal sedimentation rate (characterizing suspension stability): Take 10 mL of the original solution and centrifuge at 3000 rpm for 15 min, and measure the mass percentage of the bottom precipitate;

[0059] The results are shown in Table 1.

[0060] Table 1 Performance tests of Examples 1-4 and Comparative Examples 1-8

[0061]

[0062] As shown in Table 1, in Examples 1-4, this invention breaks through the rigid thinking of traditional foliar fertilizers that involve "passive attachment and blind release," achieving a technological leap through "organic-inorganic hybrid modification" and "multiple molecular synergy." Compared to the simple assembly of single substances in the comparative examples, this application uses KH-550 as a chemical bridge to construct a dual-gated barrier of "tea polyphenol metal coordination layer + fulvic acid" in situ on the surface of a silica carrier. This not only endows the carrier with intelligent sensing of water osmotic pressure but also gives it extremely strong leaf-targeted bio-adhesion. Simultaneously, a special seaweed oligosaccharide is prepared through "dual-enzyme hydrolysis + in-situ micro-esterification of citric acid," combined with a high-shear process, macroscopically locking the fertilizer's suspension stability and microscopically establishing a three-dimensional drought-resistant pathway from small-molecule gene induction to nano-zinc targeted catalysis. This deep coupling of material structure and preparation process achieves remarkable intelligent drought-resistant effects.

[0063] In Comparative Example 1, the fertilizer completely lost its "gating" ability by adding ordinary nano-zinc oxide directly without using the fulvic acid-tea polyphenol dual-modified carrier. The zinc release rate skyrocketed under sufficient water conditions, leading not only to early nutrient loss but also a high risk of zinc poisoning. Simultaneously, without the carrier's anchoring, the nanoparticles easily aggregated again, resulting in a sharp increase in sedimentation rate and severely impacting the formulation's shelf life. In Comparative Example 2, omitting the tea polyphenol coating on the carrier surface directly severed its adhesion to the soybean leaf villi and cuticle, reducing the leaf surface erosion resistance retention rate. Furthermore, the lack of tea polyphenols' UV shielding and free radical scavenging functions exacerbated oxidative damage to leaf cells under drought stress, significantly increasing MDA content. In Comparative Example 3, the absence of potassium fulvicate for secondary sealing of the pores left them completely open. Tests showed a zinc release rate as high as 75.5% under sufficient water conditions. The intelligent water sensing mechanism failed, preventing the "drought-triggered, on-demand release" emergency drought relief mechanism from being realized, resulting in a significantly shortened fertilizer effect cycle. In Comparative Example 4, without silane coupling agent amination treatment, tea polyphenols and fulvic acid could only adhere to the silica surface through weak physical adsorption. In the external liquid environment, this physical coating layer was easily detached, leading to uncontrolled zinc release rate under normal conditions. Furthermore, the detached organic matter reduced the system's suspension stability, resulting in a deterioration in the MDA drought resistance index. In Comparative Example 5, using un-enzymatically hydrolyzed macromolecular algae extract maintained basic physical film-forming and water-retaining properties, but the macromolecular polysaccharides could not penetrate the leaf cuticle to enter the cell interior. This resulted in the loss of the function of small-molecule algae oligosaccharides as inducers to activate endogenous drought-resistant genes in plants, causing a surge in MDA content in soybean plants and a significant reduction in physiological drought resistance. In Comparative Example 6, the lack of in-situ micro-esterification with citric acid meant that the alginic acid molecular chain ends could not provide sufficient active carboxyl groups to chemically anchor the modified carrier. This led to the loss of the "molecular bridge" between the organic liquid phase and the inorganic carrier, causing the collapse of the microscopic interpenetrating network. Macroscopically, this manifested as a sharp increase in centrifugal sedimentation rate and severe product stratification. In Comparative Example 7, no tea polyphenols were added to the liquid phase system. Although the carrier itself contained tea polyphenols, the overall surface tension and interfacial wettability of the liquid film deteriorated, resulting in a decrease in leaf retention rate. Simultaneously, the reduction in tea polyphenols that resisted strong photo-oxidation led to a deterioration in the initial drought resistance physiological index (MDA). In Comparative Example 8, by abandoning the high-shear process and using conventional stirring, the modified nanocarrier could not overcome the localized high viscosity resistance of alginate within the system. It failed to be forcibly embedded into the polymer network, instead existing freely or even agglomerated. This not only significantly increased the sedimentation rate but also hindered the effective dispersion and release of the carrier, resulting in a zinc release rate of only 63.0% under drought stress and a comprehensive reduction in drought resistance efficacy.

[0064] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a drought-resistant foliar fertilizer containing nano-zinc oxide for soybean cultivation, characterized in that: The preparation method is as follows: Deionized water is added to a reaction vessel, and after heating, enzymatically hydrolyzed alginic acid, compound amino acids, sugar alcohol complexing agent and tea polyphenols are added in sequence. After stirring, fulvic acid-tea polyphenol dual-modified carrier is added, and a high-shear emulsifier is started for shear dispersion. Organosilicon surfactant is added, the rotation speed is reduced and the temperature is lowered, and the mixture is allowed to stand for maturation to obtain the drought-resistant foliar fertilizer. The fulvic acid-tea polyphenol dual-modified carrier was prepared from an aminated carrier, an aqueous solution of tea polyphenols, ferric chloride, and an aqueous solution of potassium fulvicate. The enzymatically hydrolyzed alginic acid is prepared from algae powder, compound enzyme and citric acid monohydrate.

2. The preparation method of the drought-resistant foliar fertilizer containing nano-zinc oxide for soybean planting according to claim 1, characterized in that: The compound amino acid is a plant-derived hydrolyzed amino acid powder.

3. The preparation method of the drought-resistant foliar fertilizer containing nano-zinc oxide for soybean planting according to claim 1, characterized in that: The sugar alcohol complexing agent is obtained by combining xylitol and sorbitol.

4. The preparation method of the drought-resistant foliar fertilizer containing nano-zinc oxide for soybean planting according to claim 1, characterized in that: The preparation method of the fulvic acid-tea polyphenol dual-modified carrier is as follows: the aminated carrier is added to the aqueous solution of tea polyphenols, ferric chloride is added as a crosslinking accelerator to carry out the reaction, the aqueous solution of potassium fulvicate is added to continue the reaction, and after filtration, washing and drying, the carrier is ground to obtain the fulvic acid-tea polyphenol dual-modified carrier.

5. The method for preparing the drought-resistant foliar fertilizer containing nano-zinc oxide for soybean planting according to claim 4, characterized in that: The preparation method of the aminated carrier is as follows: porous silica is added to a nano zinc oxide ethanol dispersion, and after constant temperature shaking, it is centrifuged and dried to obtain zinc-loaded powder; the zinc-loaded powder is dispersed in an ethanol aqueous solution, silane coupling agent KH-550 is added, and the mixture is refluxed to obtain the aminated carrier.

6. The preparation method of the drought-resistant foliar fertilizer containing nano-zinc oxide for soybean planting according to claim 1, characterized in that: The method for preparing enzymatically hydrolyzed alginate is as follows: the algae powder is added to deionized water and stirred. After heating and reacting, the pH value is adjusted with sodium bicarbonate, and the compound enzyme is added for hydrolysis. The citric acid monohydrate is added, the temperature is raised and reacted, and the mixture is filtered and concentrated to obtain the enzymatically hydrolyzed alginate.

7. The method for preparing the drought-resistant foliar fertilizer containing nano-zinc oxide for soybean planting according to claim 6, characterized in that: The complex enzyme is obtained by mixing alginate lyase and cellulase at a mass ratio of 2.5-3.5:

1.

8. The method for preparing a drought-resistant foliar fertilizer containing nano-zinc oxide for soybean cultivation according to claim 2, characterized in that: The preparation method of the plant-derived hydrolyzed amino acid powder is as follows: defatted soybean powder is added into deionized water and stirred and dispersed, NaOH solution is used to adjust the pH value, neutral protease is added for enzymatic hydrolysis, citric acid solution is used to adjust the pH value of the system after heating, flavor enzyme is added for hydrolysis, and enzyme inactivation is carried out after heating, and then the supernatant is obtained by centrifugation after the system is cooled to room temperature The The supernatant is concentrated, L-proline powder is added into the concentrated solution, and the plant-derived hydrolyzed amino acid powder is obtained by drying.

9. The method for preparing the drought-resistant foliar fertilizer containing nano-zinc oxide for soybean planting according to claim 5, characterized in that: In the preparation of the zinc-loaded powder, the porous silica is added to the nano zinc oxide ethanol dispersion, and then placed in a vacuum drying oven for vacuuming. After restoring to normal pressure, it is ultrasonically dispersed, and the vacuuming-restoring-ultrasonic operation is repeated 3 times.

10. A drought resistant foliar fertilizer containing nano zinc oxide for soybean cultivation, characterized by: The drought-resistant foliar fertilizer is prepared by the preparation method described in any one of claims 1-9; the raw materials for preparing the drought-resistant foliar fertilizer include humic acid-tea polyphenol dual-modified carrier, enzymatically hydrolyzed alginic acid, compound amino acids, sugar alcohol complexing agent, tea polyphenols and organosilicon surfactant.

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