Fulvic acid-oligosaccharide supramolecular copolymer, preparation method and application thereof

Abstract

The application discloses a fulvic acid-oligosaccharide supramolecular copolymer and a preparation method and application thereof, and belongs to the field of agricultural inputs. The copolymer is a supramolecular polymer formed by non-covalent bond ordered self-assembly of fulvic acid and complex oligosaccharide monomers under weak acid conditions with pH of 3.0-5.0; the molecular weight polydispersity index PDI of the copolymer is 1.01-1.09; the complex oligosaccharide monomers include D-mannose, D-mannuronic acid, D-glucuronic acid, D-glucose, D-galactose, L-rhamnose, D-quino sugar and D-xylose. The copolymer has an ultra-narrow PDI distribution, and can effectively relieve rice yellow leaves and promote effective tillering of wheat when applied in rice or wheat cultivation.

Description

Technical Field

[0001] This application belongs to the field of agricultural input technology, specifically relating to a fulvic acid-oligosaccharide supramolecular copolymer, its preparation method, and its application. Background Technology

[0002] Fulvic acid and oligosaccharides are currently the most widely used biostimulants in agriculture, possessing multiple functions such as promoting root development, improving nutrient utilization efficiency, regulating endogenous hormone levels in crops, and enhancing stress resistance. Existing commercially available fulvic acid-oligosaccharide products are mostly simple physical compound systems of raw materials, lacking ordered molecular-level binding, and exhibit significant technical deficiencies in structural uniformity, functional stability, and application efficacy. (1) Wide molecular weight distribution and poor reproducibility of effects—The polydispersity index (PDI) of traditional compound products is generally greater than 1.20. The large range of molecular size and uneven distribution of active sites lead to asynchronous absorption rates of different components by crops, resulting in large fluctuations in field application effects and poor batch-to-batch repeatability, making it difficult to achieve standardized and precise cultivation regulation. Although attempts have been made to narrow the molecular weight distribution through membrane filtration, fractional precipitation, etc., the process costs are high and the activity loss is large, and it is still impossible to stably control the PDI below 1.10.

[0003] (2) Disordered functional group arrangement and insufficient ammonium nitrogen slow release capacity—In the physical compound system, fulvic acid and oligosaccharide molecules are randomly dispersed, and the active functional groups such as carboxyl and hydroxyl groups are arranged in a disordered manner, which affects the release of ammonium ions (NH4+) generated by urea hydrolysis in the soil. + Low complexation capacity and weak slow-release effect. After urea is applied to paddy fields, the soil accumulates high concentrations of ammonium nitrogen in a short period of time, leading to an imbalance in nitrification and a large accumulation of nitrite, which poisons the new roots of rice and causes problems such as yellowing leaves, stunted seedlings, delayed greening, and frequent occurrence of red blight after transplanting. Existing products cannot solve this problem at its root.

[0004] (3) The oligosaccharide components are simple and the tillering regulation ability is limited. Most ordinary products contain only 1-2 oligosaccharide components, which cannot form a multi-target synergistic signal regulation system. They are not able to activate the endogenous auxin and cytokinin pathways of crops, and it is difficult to stably induce the differentiation of effective low-level tillers in wheat. The yield increase effect is uncontrollable and cannot support the demand for ultra-high yield wheat cultivation. Summary of the Invention

[0005] In view of this, the primary objective of this application is to provide a fulvic acid-oligosaccharide supramolecular copolymer, which is a uniform supramolecular polymer formed by the orderly self-assembly of fulvic acid molecules and various oligosaccharide monomers in a weakly acidic environment through hydrogen bonding, π-π stacking and hydrophobic interactions. The PDI of the copolymer is stably controlled at 1.01-1.09, enabling its effective application in the regulation of nitrogen metabolism in rice, the control of nitrite toxicity, and the cultivation of wheat with high tillering and yield.

[0006] To achieve the above objectives, this application adopts the following technical solution: One aspect of this application discloses a fulvic acid-oligosaccharide supramolecular copolymer, which is a supramolecular polymer formed by the ordered self-assembly of fulvic acid and complex oligosaccharide monomers under weakly acidic conditions through non-covalent bonds. In this application, the copolymer is not a simple physical mixture, but a polymer system with a highly ordered structure spontaneously formed by weak intermolecular interactions.

[0007] In the self-assembly process, a weakly acidic environment is a key condition for achieving ordered molecular arrangement. Specifically, a weakly acidic environment allows for the appropriate protonation of fulvic acid, providing directional hydrogen bonding sites, eliminating extreme electrostatic repulsion / excessive flocculation of molecules, and thus establishing the charge basis for ordered assembly. In this application, the term "weakly acidic" refers to a pH value controlled between 3.0 and 5.0, for example, any value among 3.0, 3.5, 4.0, 4.5, and 5.0, or a range between any two values.

[0008] In this application, fulvic acid is a mixture of organic weak acids with the smallest molecular weight and highest biological activity among humic acids. It is mainly composed of aromatic polycyclic compounds containing abundant oxygen-containing functional groups (such as carboxyl groups, phenolic hydroxyl groups, quinone groups, and alcoholic hydroxyl groups) cross-linked with aliphatic carbon chains. In this application, fulvic acid specifically refers to plant-derived fulvic acid. Specific plant sources can be corn cobs, sugarcane bagasse, straw, sawdust, etc., but are not limited to these. Plant-derived fulvic acid has a small molecular weight, good water solubility, high biological activity, and no risk of heavy metal residues. More importantly, its structure contains densely packed phenolic hydroxyl and carboxyl groups, resulting in low steric hindrance and providing abundant non-covalent bonding sites, thereby enabling intermolecular recognition and ordered self-assembly with complex oligosaccharide monomers. In some specific examples, the fulvic acid is preferably corn cob-derived fulvic acid.

[0009] In this application, the described complex oligosaccharide monomer is a multi-component sugar mixture system, specifically including D-mannose, D-mannuronic acid, D-glucuronic acid, D-glucose, D-galactose, L-rhamnose, D-quinolose, and D-xylose. By having multiple monosaccharides and uronic acids coexist in specific mass ratios, they collectively participate in the construction of the supramolecular system, thereby avoiding the inability to form a multi-target synergistic signal regulation system due to a single oligosaccharide component. Multiple oligosaccharide components can enhance the activation capacity of endogenous auxin and cytokinin pathways in crops. In some specific embodiments, the mass ratio of each characteristic monosaccharide is D-mannose:D-mannuronic acid:D-glucuronic acid:D-glucose:D-galactose:L-rhamnose:D-quinolose:D-xylose = (0.5~1):(0.3~0.8):(0.2~0.5):(60~80):(0.4~0.9):(0.2~0.6):(0.8~1.5):(5~10). Through the specific ratio of this compounding, the active groups on the oligosaccharide molecular chain can achieve optimal spatial matching with the aromatic ring and functional groups of the fulvic acid molecule, promoting self-assembly.

[0010] In this application, the ratio of fulvic acid to the complex oligosaccharide monomer can be adjusted according to actual needs. A suitable ratio ensures that the fulvic acid molecule provides sufficient aromatic hydrophobic framework and hydrogen bond donor, while the oligosaccharide molecule provides a hydrophilic shell and hydrogen bond acceptor, enabling the two to form the most stable supramolecular conformation with the highest bioavailability. In some specific examples, the dry mass ratio of fulvic acid to the complex oligosaccharide monomer is (3~5):1, for example, any ratio within 3:1, 4:1, or 5:1, or a range between any two ratios.

[0011] In this application, the copolymer is characterized by gel permeation chromatography (GPC) to have a number-average molecular weight (Mn) of 24,000–25,000 Da, for example, 24,000 Da, 24,500 Da, 25,000 Da, or any value between them; a weight-average molecular weight (Mw) of 25,800–26,500 Da, for example, 25,800 Da, 26,000 Da, 26,500 Da, or any value between them; and a Z-average molecular weight (Mz) of 27,000–28,000 Da, for example, 27,000 Da, 27,500 Da, 28,000 Da, or any value between them. The molecular weight polydispersity index (PDI) is 1.01–1.09, for example, any value among 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, and 1.09, or a range between any two values.

[0012] The copolymers in this application have ultra-narrow PDI values ​​and ultra-narrow molecular weight distributions, which indicates that the supramolecular self-assembly process has high order and controllability. The resulting copolymer chain segments have relatively uniform length distributions, which is a key indicator for their stable physiological regulatory function in agricultural applications.

[0013] Furthermore, Fourier transform infrared spectroscopy (FTIR) revealed specific characteristic absorption peaks in the copolymer, confirming the existence and interaction of specific chemical bonds and functional groups within the supramolecular system. The specific characteristic peak distribution is as follows: 3344 cm - The broad and strong absorption peak at ¹ is attributed to the stretching vibration of the hydroxyl group (-OH), indicating that there are a large number of alcoholic and phenolic hydroxyl groups in the system, and that extensive intermolecular hydrogen bonds may have formed. 2902.3 cm - The absorption peak at ¹ corresponds to the C-H stretching vibration of alkane, reflecting the structural characteristics of sugar rings and aliphatic side chains; 1635.3 cm - The absorption peak at ¹ is an overlap peak of the asymmetric stretching vibration of the C=C group of the alkene and the carboxyl group, which reflects the aromatic conjugated system and carboxyl functional group in the fulvic acid skeleton. 1513.8 cm - The absorption peak at ¹ is attributed to the aromatic skeletal vibration, further confirming the introduction of the aromatic ring structure of fulvic acid. 1261.2 cm - ¹and 1056.8 cm - The absorption peak at ¹ corresponds to the C—O—C stretching vibration of the ether bond, which is a signal of the glycosidic bond and the possible ester or ether bond formed between fulvic acid and oligosaccharides. 1159.0 cm - The absorption peak at ¹ represents the C—O stretching vibration of the hydroxyl group in alcohols and phenols; 605.5 cm - The absorption peak of ¹ is a characteristic peak of haloalkanes, which may originate from trace amounts of haloalkanes remaining during the raw material extraction process or from a specific bonding environment.

[0014] The second aspect of this application discloses a method for preparing the aforementioned fulvic acid-oligosaccharide supramolecular copolymer. This method features mild process conditions, simple operation, and is easily scaled up for industrial application. The specific processing steps are as follows: Solution preparation In this step, aqueous solutions of fulvic acid with a mass fraction of 4%–8% and oligosaccharides with a mass fraction of 7.5%–9.5% are prepared. As specific examples, the mass fraction of the fulvic acid aqueous solution can be 4%, 5%, 6%, 7%, 8%, or any value between them; the mass fraction of the oligosaccharide aqueous solution can be 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, or any value between them. Appropriate solution concentrations facilitate uniform mass transfer between molecules, promote intermolecular collisions and recognition, and ensure orderly self-assembly.

[0015] pH adjustment In this step, the pH of the fulvic acid aqueous solution is adjusted to 3.0-5.0. In this application, citric acid is used as a pH adjuster. Specifically, citric acid buffers and stabilizes acidity, and also has the functions of bridging supramolecular structures with organic roots, chelating and removing impurities, and ensuring agricultural safety. This allows fulvic acid and the complex oligosaccharide monomers to complete highly ordered self-assembly at the molecular level. Furthermore, while adjusting the pH, the solution is stirred at a constant speed of 100-150 rpm to ensure that the acidity adjuster is rapidly and evenly dispersed in the solution, avoiding localized over-acidity that could lead to fulvic acid precipitation or structural damage.

[0016] Isothermal self-assembly reaction In this step, the fulvic acid aqueous solution is stirred at a constant speed of 100-150 rpm at a suitable temperature, and the oligosaccharide aqueous solution prepared above is slowly added dropwise to the fulvic acid solution.

[0017] The appropriate temperature varies depending on the production scale. Specifically, in small-volume laboratory tests, where the total amount of material is small and the diffusion distance is short, the reaction is preferably carried out at 28-30℃. In large-scale production, the reaction temperature needs to be increased to 120-190℃ to shorten the reaction time and improve batch consistency.

[0018] By providing appropriate thermal energy at suitable temperatures, the coiled skeleton of fulvic acid is unwound, while simultaneously achieving reversible reconstruction of non-covalent bonds and automatically correcting misaligned assembly structures. Furthermore, by slowly adding the mixture and stirring at a uniform speed to control local concentrations, local material imbalances are avoided, ensuring synchronous and uniform growth of supramolecular units throughout the system and preventing localized disordered aggregation. Through synergistic process conditions, hydrogen bonds, π-π stacking, and hydrophobic interactions work together to construct well-ordered, monodisperse fulvic acid-oligosaccharide supramolecular copolymers, achieving a narrow PDI (particulate density).

[0019] In this application, the rate of slow addition is not particularly limited and can be appropriately controlled according to different production scales, but the addition time should be controlled within 30-60 min, for example, it can be 30 min, 40 min, 50 min, 60 min or any value between the two. After the addition is completed, the original temperature and stirring rate are maintained, and the reaction is carried out at a constant temperature for 2-4 h (e.g. 2 h, 3 h, 4 h) to complete the ordered self-assembly process of molecules.

[0020] Filtration and Formulation In this step, after the reaction is complete, the reaction solution is filtered to remove impurities (through a 0.45 μm filter membrane) to remove any undissolved large particles or insoluble precipitates. The resulting filtrate is the liquid formulation of the fulvic acid-oligosaccharide supramolecular copolymer. In the obtained liquid formulation, the mass content of the fulvic acid-oligosaccharide supramolecular copolymer is 3% to 6%, for example, it can be 3%, 4%, 5%, or 6%.

[0021] The third aspect of this application discloses the application of the above-mentioned humic acid-oligosaccharide supramolecular copolymer in rice or wheat cultivation.

[0022] In specific examples, in rice cultivation, the supramolecular copolymer liquid formulation is applied concurrently with urea topdressing after rice transplanting, or 1-2 days before urea topdressing. The specific application method is to apply the liquid formulation with irrigation water or through drip irrigation into the field, at a rate of 500-1000 mL per acre (e.g., 500 mL, 600 mL, 700 mL, 800 mL, 900 mL, 1000 mL, etc.). The supramolecular copolymer can chelate and encapsulate the amide nitrogen in urea through its fulvic acid component, delaying nitrogen hydrolysis and reducing ammonia volatilization and leaching losses; simultaneously, the oligosaccharide component can stimulate rice root development and enhance nutrient absorption capacity, thereby significantly improving urea utilization and promoting rice tillering and dry matter accumulation.

[0023] In other examples, in wheat cultivation, the supramolecular copolymer is used in a controlled manner throughout the entire process, with the application methods for each stage as follows: Seed dressing: Use 20-30 mL of the preparation per 10 kg of wheat seeds, dilute with an appropriate amount of water, mix evenly with the seeds, and sow after drying. This step can break seed dormancy, improve germination rate and germination potential, and induce wheat to develop systemically acquired resistance (SAR) during the seedling stage, thus preventing soil-borne diseases.

[0024] Three-leaf and one-heart tillering stage: Apply as a foliar spray, using 50-80 mL of the formulation per acre, diluted with 30 kg of water before spraying. Application at this stage can promote early and rapid development of low-position tillers in wheat and increase the number of effective ears.

[0025] Jointing stage: Apply the preparation by irrigation, using 100-150 mL per acre. The jointing stage is a critical period for wheat's vegetative and reproductive growth. Irrigation of this preparation can promote thicker stems, prevent lodging, and provide sufficient chelated nutrients for spikelet differentiation.

[0026] During the grain-filling stage: Apply the formulation by foliar spraying at a rate of 60-100 mL per acre, diluted with 30 kg of water. Spraying during the grain-filling stage can delay leaf senescence, prolong the grain-filling time, promote the transport of photosynthetic products to the grains, and significantly improve the thousand-grain weight and quality.

[0027] This application has at least the following beneficial effects: This application, through supramolecular self-assembly, has for the first time stably controlled the PDI of fulvic acid-oligosaccharide polymers within the range of 1.01-1.09, far lower than the level of traditional products >1.2. The molecular size is highly uniform, the crop absorption synchronization is greatly improved, and the field application effect is stable and reproducible. It has achieved precise control of the molecular weight distribution of the product and stable and reproducible application effects between batches.

[0028] Specifically, the ordered assembly of supramolecular structures exposes active functional groups such as carboxyl and hydroxyl groups in a directional and high-density manner, which is beneficial for NH4+. + The complexation capacity is significantly improved, which can reduce the peak concentration of ammonium nitrogen and the peak accumulation of nitrite in the soil, thereby alleviating the nitrite toxicity of rice caused by urea application from the root cause, reducing the rate of yellow leaves and shortening the greening period. In addition, the complex oligosaccharide system composed of 8 characteristic monosaccharides can activate the auxin and cytokinin signaling pathways at multiple targets, precisely regulate wheat tiller differentiation, effectively increase the number of effective tillers per plant, and achieve stable and high wheat yield.

[0029] This application demonstrates that controllable assembly can be completed under weakly acidic conditions, with short process steps, low energy consumption, stable product parameters, and good batch repeatability, which can meet the needs of large-scale production. Attached Figure Description

[0030] Figure 1 This is the gel permeation chromatography (GPC) chromatogram of the product in Example 1 of this application.

[0031] Figure 2 This is the Fourier transform infrared (FT-IR) spectrum of the product in Embodiment 1 of this application.

[0032] Figure 3 This is a graph showing the results of monosaccharide composition detection for the product in Example 1 of this application. Detailed Implementation

[0033] The present application will be further illustrated below with reference to specific embodiments. It should be noted that the specific embodiments below are for illustrative purposes only and do not limit the scope of the present application in any way.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0035] In addition, unless otherwise specified, methods without detailed conditions or steps are conventional methods, and the reagents and materials used are commercially available.

[0036] Example 1: Fulvic acid-oligosaccharide supramolecular copolymer and its preparation This embodiment discloses a fulvic acid-oligosaccharide supramolecular copolymer, and the specific preparation method is as follows: S1. Weigh 40 g of dried fulvic acid material (Henan corn cob fulvic acid), dissolve it in 960 mL of deionized water, and stir until completely dissolved to obtain a 4% fulvic acid aqueous solution.

[0037] S2. Weigh 10 g of the complex oligosaccharide monomers, including 0.08 g of D-mannose, 0.05 g of D-mannuronic acid, 0.03 g of D-glucuronic acid, 7.5 g of D-glucose, 0.05 g of D-galactose, 0.03 g of L-rhamnose, 0.1 g of D-quinolose, and 2.16 g of D-xylose, and dissolve them in 100 mL of deionized water to obtain an oligosaccharide aqueous solution.

[0038] S3. Transfer the fulvic acid aqueous solution into the reaction vessel, and add 0.1 mol / L citric acid dropwise while stirring at a constant speed of 120 r / min to adjust the pH of the system to 4.0.

[0039] S4. Control the system temperature at 30℃, slowly add the oligosaccharide aqueous solution to the fulvic acid solution, and add it dropwise for 45 minutes. After the addition is completed, maintain the constant temperature and stir the reaction for 3 hours to complete the supramolecular ordered assembly.

[0040] S5. The reaction solution was filtered through a 0.45 μm microporous membrane to obtain approximately 1050 mL of liquid formulation, with a total solid content of approximately 4.76% for the supramolecular copolymer.

[0041] Among them, according to GPC testing: Mn=24542 Da, Mw=26198 Da, Mz=27743 Da, PDI=1.06748, which falls within the range of 1.01-1.09. Figure 1 ).

[0042] Infrared spectrum: at 3344 cm⁻¹ - ¹、2902.3 cm - ¹, 1635.3 cm- ¹、1513.8 cm - ¹、1261.2 cm - ¹、1056.8 cm - ¹、1159.0 cm - ¹、605.5 cm - Characteristic absorption peaks appeared at all locations (¹). Figure 2 ).

[0043] The monosaccharide composition includes eight components: D-mannose, D-mannuronic acid, D-glucuronic acid, D-glucose, D-galactose, L-rhamnose, D-quinolose, and D-xylose. Figure 3 ).

[0044] Example 2: Fulvic acid-oligosaccharide supramolecular copolymer and its preparation This embodiment discloses another fulvic acid-oligosaccharide supramolecular copolymer, and the specific preparation method is as follows: S1. Weigh 30 g of dried fulvic acid material (Henan corn cob fulvic acid), dissolve it in 970 mL of deionized water, and stir until completely dissolved to obtain a 3% fulvic acid aqueous solution.

[0045] S2. Weigh 7.5 g of the complex oligosaccharide monomers, wherein the mass ratio of each monosaccharide is the same as in Example 1, and dissolve them in 80 mL of deionized water to obtain an oligosaccharide aqueous solution.

[0046] S3. Transfer the fulvic acid aqueous solution into the reaction vessel, and add 0.1 mol / L citric acid dropwise while stirring at a constant speed of 120 r / min to adjust the pH of the system to 3.5.

[0047] S4. Control the system temperature at 28℃, slowly add the oligosaccharide aqueous solution to the fulvic acid solution, and add it dropwise for 30 minutes. After the addition is completed, maintain the constant temperature and stir the reaction for 2.5 hours to complete the supramolecular ordered assembly.

[0048] S5. The reaction solution is filtered through a 0.45 μm microporous membrane to obtain a liquid preparation with a total solid content of approximately 3.5% for the supramolecular copolymer.

[0049] Among them, GPC detection showed: Mn=24126 Da, Mw=26104 Da, Mz=28244.17 Da, PDI=1.082; the monosaccharide composition and infrared characteristic peaks were consistent with those of Example 1.

[0050] Example 3: Fulvic acid-oligosaccharide supramolecular copolymer and its preparation This embodiment refers to the implementation method of Embodiment 1, with the only difference being: in this embodiment, the mass ratio of fulvic acid to the dry basis of the complex oligosaccharide is 3:1, the mass ratio of monosaccharides within the complex oligosaccharide is D-mannose:D-mannuronic acid:D-glucuronic acid:D-glucose:D-galactose:L-rhamnose:D-quinolose:D-xylose = 0.5:0.3:0.2:60:0.4:0.2:0.8:5, the pH of the system is controlled at 3.0, the reaction temperature is 30℃, the oligosaccharide aqueous solution is added dropwise at a uniform rate for a total time of 60 min, the dropping rate is about 1.73 mL / min, and the reaction is carried out at a constant temperature for 4 h after the addition is completed.

[0051] After preparation, the liquid formulation was obtained by filtration through a 0.45 μm microporous membrane, with a solid content of approximately 3.28%.

[0052] GPC analysis showed that Mn = 24087 Da, Mw = 25895 Da, Mz = 27841 Da, and PDI = 1.075. The characteristic peaks of the infrared spectrum were consistent with those of Example 1, indicating that the monosaccharide components were intact and undegraded.

[0053] Example 4: Fulvic acid-oligosaccharide supramolecular copolymer and its preparation This embodiment refers to the implementation method of Embodiment 1, with the only difference being: in this embodiment, the mass ratio of fulvic acid to the dry basis of the complex oligosaccharide is 5:1, and the mass ratio of monosaccharides within the complex oligosaccharide is D-mannose:D-mannuronic acid:D-glucuronic acid:D-glucose:D-galactose:L-rhamnose:D-quinolose:D-xylose = 1:0.8:0.5:80:0.9:0.6:1.5:10. The pH of the system is controlled at 5.0, the reaction temperature is 30℃, the stirring speed is 150 rpm, the oligosaccharide aqueous solution is added dropwise at a uniform rate for a total time of 30 min, the dropping rate is about 3.07 mL / min, and the reaction is carried out at a constant temperature for 2 h after the addition is completed.

[0054] After preparation, the liquid formulation was obtained by filtration through a 0.45 μm microporous membrane, with a solid content of approximately 5.82%.

[0055] GPC analysis showed that Mn = 24863 Da, Mw = 26457 Da, Mz = 27926 Da, and PDI = 1.064. The characteristic peaks of the infrared spectrum were consistent with those of Example 1, indicating that the monosaccharide components were intact and undegraded.

[0056] Comparative Example 1 This comparative example uses the same implementation method as Example 1, except that step S3, which adjusts the pH, is not performed. All other process steps are the same as in Example 1.

[0057] GPC analysis showed that Mn = 22618 Da, Mw = 27942 Da, Mz = 34566 Da, and PDI = 1.235, indicating a significantly broadened molecular weight distribution. The intensity of characteristic peaks for hydroxyl, carboxyl, and ether bonds in the infrared spectrum was greatly reduced, indicating that an ordered supramolecular structure could not be formed.

[0058] Comparative Example 2 This comparative example uses the same implementation method as Example 1, except that in step S4, the oligosaccharide aqueous solution is directly poured into the fulvic acid solution, and the reaction is carried out at a constant temperature with stirring for 3 hours. All other process steps and condition parameters are the same as in Example 1.

[0059] GPC analysis showed that Mn=23157 Da, Mw=28258 Da, Mz=35294 Da, and PDI=1.220, indicating a wide molecular weight distribution. Furthermore, the characteristic absorption of ether bonds and carboxyl groups in the infrared spectrum was significantly reduced, making it impossible to form a regular and ordered supramolecular assembly.

[0060] Application Example 1: Rice Field Experiment Experimental location: rice-growing area in Taizhou, Jiangsu Province. The soil was paddy soil with a stagnant soil type. The base fertilizer was 15 kg of urea per mu. The rice variety tested was Nanjing 9108.

[0061] Experimental setup: blank control (urea only), comparative example 1, comparative example 2, example 1, example 3 and example 4, each treatment was repeated 3 times, plot area was 20 m², randomized block design.

[0062] Application method: Apply 15 kg of urea per mu as base fertilizer; when applying urea as top dressing for tillering on the 3rd day after transplanting, apply 800 mL / mu of each treatment preparation with water.

[0063] Testing methods: Fresh soil samples from the 0-20 cm topsoil layer were collected from each plot on the 7th day after topdressing. The nitrite content of the soil was determined according to NY / T 1121.10-2021 "Soil Testing Part 10: Determination of Nitrate Nitrogen, Nitrite Nitrogen and Ammonium Nitrogen in Soil". The number of days for rice to turn green was determined according to the seedling greening criteria in NY / T 1615-2008 "Rice Cultivation Technical Specifications". The number of rice plants with yellow leaves was counted according to the yellow leaf determination rules in DB32 / T 3640-2019 "Green Control Technical Specifications for Rice Red Wilt". The incidence rate survey of rice red wilt was carried out in accordance with NY / T 2186-2012 "Rice Disease and Pest Survey Specifications".

[0064] The results are shown in Table 1.

[0065] Table 1 Results of rice field trials

[0066] As can be seen from the results in Table 1, the liquid formulation in the examples has significantly better effects than the comparative formulation in inhibiting soil nitrite accumulation, promoting rice greening, and resisting toxicity. It can solve the problem of yellowing leaves and stunted seedlings of rice caused by urea application from the root.

[0067] Application Example 2: Wheat Tillering Yield Trial Experimental location: Weifang Wheat Experimental Base, Shandong Province. The tested variety was Jimai 22. Single-plant planting method was adopted (to eliminate competition between plants), with a plant spacing of 20 cm × 20 cm.

[0068] Experimental setup: blank control (without copolymer liquid formulation), comparative example 1, comparative example 2, example 1, example 3 and example 4, each treatment was repeated 3 times, plot area 2 m².

[0069] Application method: Follow the wheat application protocol described in this application, with consistent dosage for each treatment, as detailed below: ① Seed dressing stage: Use 25 mL of liquid preparation for every 10 kg of wheat seeds. Dilute with water, dress the seeds, dry them, and then sow them. ② During the three-leaf-one-heart tillering stage: Apply 65 mL of the preparation per mu, diluted with 30 kg of water, and spray on the leaves; ③ Jointing stage: Apply 125 mL of the preparation per mu (unit of land area) with irrigation water; ④ Grain filling period: Apply 80 mL of the preparation per mu, diluted with 30 kg of water and sprayed on the leaves.

[0070] Testing indicators: number of effective tillers per plant at maturity, tillering efficiency, and grain yield per plot.

[0071] The results are shown in Table 2.

[0072] Table 2 Results of wheat tillering yield experiment

[0073] The results in Table 2 show that the fulvic acid-oligosaccharide supramolecular copolymer in this application can significantly improve the effective tillering and tillering efficiency of wheat, increase the yield of the plot, and has a significant effect on increasing yield and promoting tillering.

[0074] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A fulvic acid-oligosaccharide supramolecular copolymer, characterized in that, The copolymer is a supramolecular polymer formed by the non-covalent ordered self-assembly of fulvic acid and complex oligosaccharide monomers under weakly acidic conditions of pH 3.0~5.0; The copolymer has a number-average molecular weight Mn of 24,000-25,000 Da, a weight-average molecular weight Mw of 25,800-26,500 Da, a Z-average molecular weight Mz of 27,000-28,000 Da, and a molecular weight polydispersity index (PDI) of 1.01-1.

09. The complex oligosaccharide monomers include D-mannose, D-mannuronic acid, D-glucuronic acid, D-glucose, D-galactose, L-rhamnose, D-quinolose, and D-xylose.

2. The fulvic acid-oligosaccharide supramolecular copolymer as described in claim 1, characterized in that, The dry weight ratio of the fulvic acid and the complex oligosaccharide monomer is (3~5):

1.

3. The fulvic acid-oligosaccharide supramolecular copolymer as described in claim 1, characterized in that, In the complex oligosaccharide monomer, the mass ratio of each characteristic monosaccharide is D-mannose:D-mannuronic acid:D-glucuronic acid:D-glucose:D-galactose:L-rhamnose:D-quinolose:D-xylose = (0.5~1):(0.3~0.8):(0.2~0.5):(60~80):(0.4~0.9):(0.2~0.6):(0.8~1.5):(5~10).

4. The fulvic acid-oligosaccharide supramolecular copolymer according to claim 1, characterized in that, The copolymer exhibits the following characteristic absorption peak in Fourier transform infrared spectroscopy: 3344 cm⁻¹ - The hydroxyl stretching vibration at ¹, 2902.3 cm⁻¹ - The C-H stretching vibration of the alkane at position ¹, 1635.3 cm⁻¹ - The olefin C=C at position ¹ exhibits asymmetric stretching vibration with the carboxyl group, at 1513.8 cm⁻¹. - The aromatic skeletal vibration at position ¹, 1261.2 cm⁻¹ - ¹and 1056.8 cm - ¹ The ether bond C—O—C stretching vibration, 1159.0 cm⁻¹ - The C-O stretching vibration of the phenolic hydroxyl group at position ¹ and 605.5 cm⁻¹ - ¹ Characteristic peaks of halogenated hydrocarbons.

5. The fulvic acid-oligosaccharide supramolecular copolymer as described in claim 1, characterized in that, The fulvic acid is plant-derived fulvic acid; Optionally, the fulvic acid is corn cob plant-derived fulvic acid.

6. A method for preparing fulvic acid-oligosaccharide supramolecular copolymers, characterized in that, Includes the following steps: Prepare aqueous solutions of humic acid with a mass fraction of 4% to 8% and oligosaccharides with a mass fraction of 7.5% to 9.5%, respectively. Adjust the pH of the fulvic acid aqueous solution to 3.0-5.0; At a suitable temperature, the oligosaccharide aqueous solution is slowly added dropwise to the fulvic acid solution while stirring at a constant speed of 100-150 rpm for 30-60 min. After the addition is completed, the temperature and stirring rate are maintained, and the reaction is carried out at a constant temperature for 2-4 h to complete the ordered self-assembly of molecules. The suitable temperature is 28-30℃ in the laboratory and 120-190℃ in large-scale production. After the reaction is complete, the reaction solution is filtered to remove impurities, and the filtrate is the liquid preparation of the humic acid-oligosaccharide supramolecular copolymer as described in claims 1-5.

7. The preparation method according to claim 6, characterized in that, In the liquid formulation, the mass content of fulvic acid-oligosaccharide supramolecular copolymer is 3% to 6%.

8. The preparation method according to claim 6, characterized in that, The pH of the fulvic acid aqueous solution was adjusted using citric acid, while the solution was stirred at a constant speed of 100-150 rpm.

9. The application of the fulvic acid-oligosaccharide supramolecular copolymer as described in any one of claims 1-5 in rice or wheat cultivation.

10. The application as described in claim 9, characterized in that, The application method of the fulvic acid-oligosaccharide supramolecular copolymer is as follows: In rice cultivation, it is applied when applying urea after transplanting, or 1-2 days before applying urea; the liquid preparation of fulvic acid-oligosaccharide supramolecular copolymer is applied with water by flushing or drip irrigation, with a dosage of 500-1000 mL per mu. Alternatively, in wheat cultivation, a full-process control approach can be adopted, including: Seed dressing stage: Dilute 20-30 mL of liquid preparation with water for every 10 kg of wheat seeds, mix evenly, dry and then sow; During the tillering stage of three leaves and one heart: apply as a foliar spray, using 50-80 mL of the preparation per acre, diluted with 30 kg of water; During the jointing stage: apply with irrigation water, using 100-150 mL of the preparation per acre; Grain filling stage: Foliar spray, 60-100 mL of the preparation per acre, diluted with 30 kg of water.

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