Controlled-release nitrogen fertilizer containing organic acid salt signal substance

Abstract

This invention discloses a controlled-release nitrogen fertilizer containing organic acid salt signaling substances. From the inside out, it comprises urea particles, a cross-linked material-trace element mixture, molten urea, and a bio-based polyurethane coating material. The cross-linked material-trace element mixture is a porous cross-linked material loaded with trace elements. The porous cross-linked material is obtained by cross-linking alginic acid and organic acid salts through a cross-linking agent. The organic acid salts are selected from at least one of sodium citrate, sodium fumarate, sodium maleate, sodium malonate, and sodium succinate. The trace elements are selected from at least one of zinc, cobalt, molybdenum, and iron. This invention, through alginic acid-organic acid salt cross-linking, precise loading of trace elements, and multi-layer coating technology, produces a novel controlled-release fertilizer that combines pH responsiveness, environmental resistance, and high nutrient utilization. Nutrient release can be dynamically controlled according to soil pH and crop needs, reducing nutrient loss and environmental pollution, meeting the needs of green agriculture development, and providing an innovative solution for improving fertilizer utilization and crop yield.

Description

Technical Field

[0001] This invention relates to the field of novel fertilizer technology, specifically to a controlled-release nitrogen fertilizer containing an organic acid salt signaling substance. Background Technology

[0002] Corn, wheat, and rice, as vital global food crops, are crucial for food security due to their high and stable yields. Nitrogen fertilizer, as the primary means of supplementing nitrogen, is widely used in agricultural production, significantly improving crop yield and quality. However, the average utilization rate of nitrogen fertilizer globally is low, mainly due to several reasons. Firstly, nitrogen is easily lost in its various forms; ammonium and nitrate ions are easily transformed, leached, or volatilized in the soil, leading to nitrogen loss. Secondly, the complex soil environment, including clay minerals, organic matter, and microbial activity, affects nitrogen availability, making it difficult for crops to fully absorb and utilize it. Low nitrogen fertilizer utilization leads to nitrogen excess in the soil, resulting in thinner crop cell walls, weaker tissues, reduced stress resistance, and increased risk of pests and diseases. It also affects the absorption of micronutrients such as zinc and iron, causing yield reduction and decreased fruit quality. Excessive nitrogen can also easily lead to soil acidification and salinization, releasing ammonia or nitric acid gases, which are toxic to the crop growth environment. Therefore, the rational application of nitrogen fertilizer, improving utilization efficiency, and reducing excessive application are key to ensuring sustainable agricultural development.

[0003] Nutrient signaling molecules can influence nitrogen uptake and assimilation in plants by regulating the expression of genes related to nitrogen use. These signaling molecules act as sensors of nitrogen status within plants, triggering a series of gene expression changes that regulate root preference for nitrogen forms and nitrogen transport and distribution within the plant. Simultaneously, plants can recruit specific microbial communities that participate in nitrogen transformation processes in the soil. Through root secretions such as organic acids, plants can attract microorganisms with nitrogen-fixing, nitrification, and denitrification functions. These microorganisms can transform nitrogen forms in the soil, for example, converting atmospheric nitrogen (N2) into plant-available ammoniacal nitrogen (NH4). + ) or nitrate nitrogen (NO3) - Under the action of microorganisms, nitrogen in the soil is absorbed and assimilated by plants and stored in the plant body in the form of organic nitrogen. During plant growth, some organic nitrogen is returned to the soil through root secretions, decomposition of plant residues, and metabolic excretion, becoming part of the soil organic matter, thus affecting soil fertility and microbial activity. This process is a very important link in the nitrogen cycle, ensuring a sustainable supply of soil nitrogen and the health of the ecosystem. Therefore, nutrient signaling substances regulate plant gene expression, promote the transformation and absorption of nitrogen by microorganisms, and return organic nitrogen to the soil through the interaction between plants and microorganisms, thereby maintaining the nitrogen cycle and soil fertility.

[0004] Patent document CN118271130A discloses a fertilizer composition for reducing fertilizer usage and increasing efficiency, and its application. This invention utilizes acetate, oxalate, and phosphate to prepare a special fertilizer for Ligusticum chuanxiong cultivation. This fertilizer can reduce fertilizer usage and improve fertilizer utilization. However, it does not use the aforementioned organic acid salts as nitrogen signaling substances, and the form (e.g., solid or liquid) of its raw material fertilizer composition is unstable, which will affect the storage stability and application effect of the fertilizer. Organic acid salts have poor thermal stability and are prone to decomposition or hydrolysis at high temperatures; in addition, oxalates such as calcium oxalate are prone to crystal transformation and structural instability at high temperatures; while sodium citrate has a high critical relative humidity and is prone to adhesion after absorbing moisture. Furthermore, some organic acid salts, when in long-term contact with carriers (such as bentonite), experience a decline in slow-release performance. Therefore, the application of organic acid salts as a single component or in combination lacks an appropriate environmental matrix, cannot dynamically regulate the nutrient release rate according to soil pH, and is difficult to meet the needs of crops at different growth stages, resulting in low fertilizer utilization and potentially causing soil nutrient imbalance. Therefore, there is a need for a controlled-release nitrogen fertilizer that uses organic acid salts as nitrogen signaling substances to give the fertilizer good thermal stability and prevent the signaling substances from decomposing or deteriorating during the high-temperature heating process of fertilizer preparation, thereby maintaining the quality and effectiveness of the fertilizer. Summary of the Invention

[0005] To address the aforementioned limitations of existing technologies, the present invention aims to provide a controlled-release nitrogen fertilizer containing organic acid salt signaling substances. This invention utilizes alginate-organic acid salt crosslinking, precise micronutrient loading, and multilayer coating technology to prepare a novel controlled-release fertilizer that combines pH responsiveness, environmental resistance, and high nutrient utilization efficiency. In agricultural production, nutrient release can be dynamically controlled according to soil pH and crop requirements, reducing nutrient loss and environmental pollution, meeting the needs of green agriculture development, and providing an innovative solution for improving fertilizer utilization and crop yield.

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

[0007] In a first aspect, the present invention provides a controlled-release nitrogen fertilizer containing an organic acid salt signaling substance, comprising, from the inside out, urea particles, a cross-linked product-trace element mixture, molten urea, and a bio-based polyurethane coating material;

[0008] The crosslinker-trace element mixture is a porous crosslinked material loaded with trace elements;

[0009] The porous cross-linked material is obtained by cross-linking alginic acid and organic acid salts with a cross-linking agent;

[0010] The organic acid salt is selected from at least one of sodium citrate, sodium fumarate, sodium maleate, sodium malonate, and sodium succinate;

[0011] The trace element is selected from at least one of zinc, cobalt, molybdenum, and iron.

[0012] Preferably, the porous crosslinked material is prepared by the following method:

[0013] Alginic acid was dissolved in deionized water, and the pH was adjusted to 6.5 to obtain an alginic acid solution. Organic acid salts were dissolved in deionized water to obtain an organic acid salt solution. The organic acid salt solution was slowly added to the alginic acid solution and stirred. After stirring evenly, a crosslinking agent solution was added dropwise. The mixture was stirred and reacted at room temperature. After standing and solidifying, a uniform gel was formed. The gel was filtered, washed, and freeze-dried to obtain a porous crosslinked material.

[0014] Preferably, the concentration of the alginate solution is 3 wt%; the concentration of the organic acid salt solution is 2-10 wt%; and the molar ratio of the organic acid salt to the alginate is 1:0.5-2.

[0015] Preferably, the crosslinking agent solution comprises CaCl2 solution, EDC, and NHS; the concentration of the CaCl2 solution is 2 wt%; the Ca... 2+ The molar ratio of EDC and NHS is 1:5:2; the CaCl2 contains Ca 2+ The molar ratio of COO⁻ contained in alginate is 3:10.

[0016] Preferably, the stirring reaction time is 30 min; the static curing time is 12 h; the freeze-drying temperature is -50℃ and the time is 24 h; and the pore size of the porous cross-linked material is 50~200 nm.

[0017] Preferably, the crosslinker-trace element mixture is obtained by immersing a porous crosslinker material in a solution containing trace elements and then drying it.

[0018] Preferably, the solution containing trace elements is selected from at least one of zinc sulfate solution, ferric chloride solution, sodium molybdate solution, and cobalt nitrate solution; the mass ratio of the porous crosslinking material to the trace elements is 10:1; the impregnation pressure is -0.1 MPa and the time is 30 min; the drying is carried out at 60°C until the moisture content is 5%.

[0019] Preferably, the controlled-release nitrogen fertilizer containing organic acid salt signaling substances is prepared by the following method:

[0020] (1) The cross-linked material-trace element mixture is mixed with urea particles and PVA solution is sprayed as an adhesive to make the cross-linked material-trace element mixture uniformly coat the surface of urea particles, thus obtaining urea particles coated with cross-linked material-trace element mixture.

[0021] (2) Molten urea is atomized and sprayed onto the surface of urea particles to form a dense layer, thereby obtaining coated urea particles;

[0022] (3) The bio-polyurethane prepolymer is sprayed onto the surface of coated urea particles and cured to obtain controlled-release nitrogen fertilizer containing organic acid salt signaling substances.

[0023] Preferably, the mass ratio of the crosslinker-trace element mixture to urea particles is 1:5; the concentration of the PVA solution is 5wt%; the mass ratio of molten urea to urea particles coated by the crosslinker-trace element mixture is 1:10; the biopolyurethane prepolymer is synthesized from castor oil-based polyol and hexamethylene diisocyanate, and prepared with acetone as a solvent; the mass ratio of the biopolyurethane prepolymer to coated urea particles is 1:15.

[0024] The biopolymer polyurethane prepolymer is prepared into a 30 wt% solids solution using acetone as a solvent and applied via atomized spraying. A second aspect of the invention provides the use of an organic acid salt signaling substance in at least one of the following 1) to 5):

[0025] 1) Improve nitrogen fertilizer utilization rate;

[0026] 2) Improve Rhizobiales Relative abundance;

[0027] 3) Inhibits denitrifying bacteria Burkholderiales;

[0028] 4) Enrichment of growth-promoting bacteria Sphingomonas and Pseudomonas Relative abundance;

[0029] 5) Improve pH responsiveness.

[0030] The beneficial effects of this invention are:

[0031] (1) The present invention prepares a novel controlled-release fertilizer through alginate-organic acid acid salt crosslinking, precise loading of trace elements, and multilayer coating technology, which has the characteristics of pH responsiveness, environmental resistance, and high nutrient utilization efficiency. In agricultural production, nutrient release can be dynamically controlled according to soil pH and crop needs, reducing nutrient loss and environmental pollution, which meets the needs of green agricultural development and provides an innovative solution for improving fertilizer utilization and crop yield.

[0032] (2) The alginate used in this invention is derived from marine brown algae resources. Its natural colloidal properties not only enhance the slow-release performance of fertilizers, but also strengthen nitrogen signal transmission by stimulating the activity of root exudates. In addition, this technology provides a green solution to reduce nearshore eutrophication caused by the loss of land-based nitrogen fertilizers by integrating marine biomass resources, and embodies the sustainable development concept of coordinated utilization of land and sea resources.

[0033] (3) This invention combines the synergistic effects of controlled-release nitrogen fertilizer and nutrient signaling substances. Compared with traditional controlled-release nitrogen fertilizer, the crop-specific controlled-release nitrogen fertilizer containing nitrogen signaling substances can release nitrogen and continuously release nutrient signaling substances into the soil. On the one hand, it can meet the crop's demand for nitrogen nutrients, and the released nutrient signaling substances can regulate the metabolic activities of root cells and enhance the root system's ability to absorb soil nutrients, thereby improving the crop's nitrogen utilization efficiency. On the other hand, the marine extract alginic acid can stimulate plant roots to secrete organic acids, which, together with the organic acid salts in this invention, can regulate the rhizosphere pH value, enhance the solubility and availability of trace elements in the soil, and recruit specific rhizosphere microorganisms, which, together with the organic acid salts, can promote nitrogen activation, reduce nitrogen loss, and improve nitrogen utilization efficiency. In addition, the nutrient signaling substances and alginic acid have a synergistic effect, which can activate plant endogenous hormones, promote the transport of photosynthetic products to grains, improve grain filling efficiency, and thus increase crop yield, resulting in high yield and high quality. Attached Figure Description

[0034] Figure 1 Comparison of nitrogen release curves of fertilizers in each group with the nitrogen requirement pattern of maize;

[0035] Figure 2 Nitrogen release dynamics in Example 1 in soils with different pH values;

[0036] Figure 3 Corn yield under different fertilizer treatments;

[0037] Figure 4 Rhizosphere microbial community analysis in field experiments: (a) order level; (b) genus level. Detailed Implementation

[0038] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, 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 pertains.

[0039] As described in the background section, organic acid salts have poor thermal stability and are prone to decomposition or hydrolysis at high temperatures. Furthermore, oxalates such as calcium oxalate are susceptible to crystal transformation and structural instability at high temperatures. Sodium citrate has a high critical relative humidity and tends to stick together after absorbing moisture. Some organic acid salts also experience a decline in slow-release performance due to prolonged contact with carriers (such as bentonite). Therefore, the application of organic acid salts as single components or in combination lacks an appropriate environmental matrix, making it impossible to dynamically regulate nutrient release rates based on soil pH. This makes it difficult to meet the needs of crops at different growth stages, resulting in low fertilizer utilization and potentially causing soil nutrient imbalances.

[0040] Based on this, the purpose of this invention is to provide a controlled-release nitrogen fertilizer containing an organic acid salt signaling substance. In this invention, the nutrient signaling substance is an organic acid salt, whose functional group mainly exists in the form of sodium carboxylate (-COONa), with two sodium carboxylate groups connected on both sides of a carbon bond. The nutrient signaling substance is mixed with trace elements such as zinc, cobalt, molybdenum, and iron to improve nitrogen utilization, as well as marine extract alginic acid, to form a composite cross-linked substance. A dense layer of molten urea is formed outside the cross-linked substance coating layer, making the fertilizer particles round and smooth. Then, a layer of bio-based polyurethane membrane is sprayed onto the coating surface, thereby preparing a controlled-release nitrogen fertilizer containing a nitrogen signaling substance. Cross-linking organic acid salts with alginic acid helps to enhance controlled release and improve environmental responsiveness. The cross-linked network can adjust the porosity, controlling the release rate of nutrients (such as nitrogen, phosphorus, and potassium) through diffusion resistance. For example, the "eggbox" structure formed by cross-linking alginic acid with calcium ions can extend the urea release cycle to 60–90 days. The cross-linked material (such as pH-sensitive polymers) can dynamically adjust the network structure according to soil conditions (such as pH and humidity) to achieve intelligent controlled release. Alginic acid contains β-D-mannuronic acid (M) and α-L-guluronic acid (G), which are linked by 1→4 glycosidic bonds to form a linear polysaccharide. The molecular chain is rich in carboxylic acid groups (-COOH, pKa≈3.5). The carboxyl groups of the G units readily form "eggbox" structures between adjacent chain segments, serving as core sites for ionic cross-linking. Organic acid salts such as sodium citrate (C6H5O7) 3 ⁻), Sodium fumarate (C4H2O4) 2 ⁻), Sodium succinate (C4H4O4) 2 The anionic structure of the alginate contains carboxyl groups (-COO⁻) and some also contain hydroxyl groups (-OH), which can form a synergistic coordination with the carboxyl groups of alginate. Under pH 6.0-6.5 conditions, the cross-linked network forms a dense structure, significantly improving mechanical strength (compressive strength >5MPa), effectively inhibiting the penetration of small molecules (such as water molecules), delaying nutrient diffusion, and reducing nitrogen release rate to <0.5mg / cm²·h. It also significantly improves thermal stability (decomposition temperature increases from 180℃ to 240℃) and hygroscopic resistance (hygroscopic rate <3% after 30 days of storage at 40℃ / 75% RH).

[0041] When the soil pH is <5 (acidic soil), the carboxyl groups of alginate are partially protonated, and the cross-linked network swells (swelling rate >150%), accelerating nutrient release at a rate >2 mg / cm²·h. Under alkaline conditions of pH 7.0-8.5, the carboxyl groups are fully dissociated, forming a stable, high-strength controlled-release membrane, enabling the slow release of nutrients.

[0042] This invention combines the synergistic effects of controlled-release nitrogen fertilizer and nutrient signaling substances. Compared to traditional controlled-release nitrogen fertilizer, this crop-specific controlled-release nitrogen fertilizer containing nitrogen signaling substances releases nitrogen while continuously releasing nutrient signaling substances into the soil. On the one hand, it meets the crop's nitrogen nutrient requirements, and the released nutrient signaling substances can regulate the metabolic activities of root cells, enhancing the root system's ability to absorb soil nutrients and thus improving the crop's nitrogen utilization efficiency. On the other hand, the marine extract alginic acid can stimulate plant roots to secrete organic acids, which, together with the organic acid salts in this invention, regulate the rhizosphere pH value, enhance the solubility and availability of trace elements in the soil, and recruit specific rhizosphere microorganisms, which, together with the organic acid salts, promote nitrogen activation, reduce nitrogen loss, and improve nitrogen utilization efficiency. In addition, the nutrient signaling substances and alginic acid have a synergistic effect, activating endogenous plant hormones, promoting the transport of photosynthetic products to grains, improving grain filling efficiency, and thus increasing crop yield, resulting in high yield and high quality.

[0043] This invention constructs a controlled-release nitrogen fertilizer system through the synergistic effect of multiple components. Using coating technology, it enables simultaneous sowing of crop seed fertilizer. Centered on nutrient signaling substances, it activates insoluble phosphorus and iron in the soil through the rhizosphere acidification effect mediated by carboxylate ions. Simultaneously, it upregulates nitrogen transporter gene expression to enhance root nitrogen uptake capacity, stimulating crop roots and promoting efficient nitrogen absorption and utilization. Alginic acid, a marine extract, activates the MAPK signaling pathway through oligosaccharide fragments to promote lateral root development. Its three-dimensional network structure forms a high-strength controlled-release membrane through hydrogen bonds and ionic cross-linking. The abundant carboxyl groups in its molecular chain, through Ca2+, promote lateral root development. 2+Cross-linking forms an 'eggbox' structure, which, combined with the synergistic coordination of organic acid salts, self-assembles to construct a three-dimensional network framework, forming a high-strength controlled-release membrane with pH responsiveness. This delays the nutrient release cycle to 60-70 days and simultaneously drives the transport of photosynthetic products to the grain by upregulating sucrose transport genes. Micronutrients, as cofactors of nitrogen metabolism enzymes, chelate with organic acid salts to form stable complexes, preventing soil fixation and improving bioavailability. During high-temperature granulation, the active ingredients are protected from thermal decomposition, and their cross-linking structure with alginic acid further optimizes the slow-release kinetics. The outer layer of bio-based polyurethane membrane precisely regulates nitrogen release through a hydrophobic-hydrophilic microphase separation structure, matching the nutrient requirements of maize from the jointing stage to the grain-filling stage. Its biodegradability and the adsorption and interception capacity of alginic acid synergistically reduce the total nitrogen concentration in the Yellow River runoff, significantly alleviating the risk of near-shore eutrophication, and ultimately achieving the three-in-one goal of "increased production, increased efficiency, and reduced emissions" in agricultural green transformation. Furthermore, compared to the drawbacks of ordinary coated nitrogen fertilizer granules having uneven surfaces and requiring a large amount of coating material, this invention mixes nutrient signaling substances with trace elements such as zinc, cobalt, molybdenum, and iron that improve nitrogen utilization, as well as marine extract alginic acid to form a composite cross-linking substance. A dense layer of molten urea is formed outside the cross-linking substance coating layer, making the fertilizer granules round and smooth, improving the smoothness of the fertilizer surface, reducing the amount of coating material required, and lowering production costs.

[0044] The combined treatment of alginate and sodium organic acid can increase starch accumulation and 100-kernel weight in corn kernels, and its synergistic effect is significantly better than that of a single component. In addition, the three-dimensional network structure of alginate can form a high-strength controlled-release membrane. Combined with the slow-release properties of bio-based polyurethane, the nitrogen release cycle can be precisely matched with the fertilizer requirements of corn from the jointing to the grain-filling stage, thereby improving fertilizer utilization.

[0045] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0046] The test materials used in the embodiments of this invention are all conventional test materials in the art and can be purchased through commercial channels.

[0047] Example 1: Preparation of controlled-release nitrogen fertilizer containing organic acid salt signaling substances

[0048] (1) Cross-linked product-trace element mixture

[0049] 3g of alginate powder with a degree of polymerization of 50-2000 was added to 97g of deionized water and slowly dissolved under stirring at 40℃ and 300rpm. The initial pH was adjusted to 6.5 with 0.1M NaOH to prepare a 3 wt% alginate solution. 2.5g of sodium citrate and 1.0g of sodium fumarate were dissolved in 96.5g of deionized water to prepare a 100g organic acid salt solution (sodium citrate concentration 2.5wt%, sodium fumarate concentration 1.0wt%). Under stirring, the 100g organic acid salt solution was slowly added to the 100g alginate solution, and the mixture was stirred at 300rpm for 10 minutes. Then, 28.3g of a 2 wt% CaCl2 solution (containing 0.566g CaCl2, nCa...) was gradually added. 2+ A composite system consisting of 0.0051 mol of EDC, 4888 mg of EDC (0.0255 mol), and 1174 mg of NHS (0.0102 mol) was prepared. The mixture was stirred at room temperature (25℃) for 30 minutes and allowed to stand for 12 hours to solidify, forming a homogeneous gel. After the reaction was complete, the crosslinking product was separated by filtration or centrifugation, washed with deionized water to remove unreacted impurities, and then freeze-dried (-50℃, 24 h) to obtain porous crosslinked particles with a pore size of 50-200 nm and a specific surface area >25 m². 2 / g.

[0050] Porous cross-linked particles were mixed with a trace element solution (ZnSO4 solution, FeCl3 solution, sodium molybdate solution, and cobalt nitrate solution were mixed in a molar ratio of zinc, cobalt, molybdenum, and iron of 1:0.2:0.1:0.5) at a mass ratio of 10:1. The mixture was impregnated under a vacuum of -0.1 MPa for 30 minutes to allow the trace elements to be fully adsorbed into the pores of the cross-linked particles. The mixture was then dried at 60°C until the moisture content was <5%, yielding a uniformly dispersed cross-linked-trace element composite.

[0051] (2) Urea particle coating and molten urea spraying

[0052] A crosslinker-trace element mixture with a particle size of 0.5-1 mm and urea particles with a particle size of 2-3 mm were added to a fluidized bed coating machine at a mass ratio of 1:5. A 5 wt% PVA solution (polyvinyl alcohol PVA-1788 powder was added to deionized water at 80℃, soaked and swollen at room temperature for 30 minutes, then magnetically stirred at 500 rpm for 60 minutes in an 80℃ water bath until completely dissolved, and cooled to 25℃ to form a transparent viscous solution) was sprayed as a binder. The spraying rate was controlled at 5 mL / min and the atomization pressure at 0.3 MPa to make the mixture uniformly coat the surface of the urea particles, thus obtaining urea particles coated with the crosslinker-trace element mixture.

[0053] Molten urea (140℃) is atomized and sprayed onto the surface of urea particles to coat the crosslinker-trace element mixture. The mass ratio of molten urea to the crosslinker-trace element mixture coating the urea particles is 1:10, forming a dense layer of 50–100 μm to obtain coated urea particles.

[0054] (3) Bio-based polyurethane membrane wrapping

[0055] A bio-based polyurethane prepolymer was synthesized by reacting castor oil-based polyol (hydroxyl value 160 mg KOH / g) with hexamethylene diisocyanate (HDI) at a molar ratio of NCO:OH = 2:1 and reacting at 70°C for 3 hours. The bio-based polyurethane prepolymer solution was then prepared by diluting the prepolymer with acetone to a solid content of 30 wt%.

[0056] A bio-based polyurethane prepolymer solution and coated urea granules were added to a fluidized bed coating machine at a mass ratio of 1:15. The preheating temperature was controlled at 50℃, the atomization pressure at 0.3 MPa, and the hot air flow rate at 40 m³ / h. 3 Spraying is performed at an air inlet temperature of 60℃ for 2 hours, and the coating is cured at 60℃ to form a uniform outer coating film with a thickness of 20-30μm, ultimately yielding a controlled-release nitrogen fertilizer containing organic acid salt signaling substances.

[0057] Comparative Example 1

[0058] 1000g of urea particles with a particle size of 2-3mm were placed in a fluidized bed and sprayed with a bio-based polyurethane prepolymer solution with a solid content of 30% (preparation method is the same as step (3) in Example 1). The mass ratio of bio-based polyurethane prepolymer solution to urea particles was 1:15. The solution was cured at 60°C for 2 hours to form a uniform outer coating film with a thickness of 20-30 μm, thus obtaining coated urea.

[0059] Comparative Example 2

[0060] 1000g of urea particles with a particle size of 2-3mm were placed in a fluidized bed. First, 100g of organic acid salt solution (2.5wt% sodium citrate + 1wt% sodium fumarate, 3.5g total organic acid salt) was sprayed on. Then, a bio-based polyurethane prepolymer solution with a solid content of 30% was sprayed on (the preparation method is the same as step (3) in Example 1). The mass ratio of bio-based polyurethane prepolymer solution to urea particles was 1:15. The solution was cured at 60℃ for 2 hours to form a uniform outer coating film with a thickness of 20-30 μm, thus obtaining coated urea.

[0061] Comparative Example 3

[0062] 1000g of urea particles with a particle size of 2-3mm were placed in a fluidized bed. First, 100g of 3wt% alginate solution was sprayed on, followed by a 30% solids content bio-based polyurethane prepolymer solution. The mass ratio of bio-based polyurethane prepolymer solution to urea particles was 1:15. The mixture was cured at 60℃ for 2 hours to form a uniform outer coating film with a thickness of 20-30 μm, thus obtaining coated urea.

[0063] Comparative Example 4

[0064] The difference from Example 1 is that no trace elements were added. The final product was a controlled-release nitrogen fertilizer containing organic acid salt signaling substances.

[0065] Test Example 1: Static Water Test

[0066] Grouped comparative examples 1 and 4.

[0067] The temperature was set at 25℃, the solution was deionized water (pH 6.5), the fertilizer dosage was 5g / group (3 replicates), the sampling intervals were 1, 3, 7, 14, 21, 28, 35, 42, 49, 56, 63, and 70 days, and the detection method was the Kjeldahl method.

[0068] The results measured in Experiment Example 1 can be expressed as follows: Figure 1 Comparison of nitrogen release curves of fertilizers in each group with nitrogen requirement patterns of maize.

[0069] During the seedling stage (0-20 days), Example 1's release rate of 15.0% precisely matched the nitrogen requirement of 13%, while the comparative treatments showed a serious imbalance—Comparative Example 1 released 40.3%, and Comparative Example 2 released 64.7%, leading to the risk of excessive vegetative growth; Comparative Example 3 released only 9.5%, limiting seedling development. This indicates that the molten urea layer in Example 1 provided a stable release of 0.29% / day during this stage, perfectly matching the initial requirement of 0.25% / day for corn.

[0070] During the jointing stage (21-35 days), the release rate of Example 1 (57.1%) was moderately higher than the nitrogen requirement of 55%, meeting the peak growth of stems and leaves; while the release rates of Comparative Example 1 (88.3%) and Comparative Example 2 (95.4%) were wasteful; and the release rate of Comparative Example 3 (50.7%) limited biomass accumulation. This indicates that during this stage, the cross-linked layer in Example 1 increased the release slope to 1.60% / day through pH response, precisely matching the nitrogen requirement slope of 1.43% / day.

[0071] During the tasseling stage (36-49 days), the release rate of 89.7% in Example 1 closely matched the nitrogen requirement of 87%, ensuring ear differentiation; while the release rates of 96.1% in Comparative Example 1 and 97.1% in Comparative Example 2 were prematurely depleted; and the release rate of 81.7% in Comparative Example 3 inhibited ear development. This indicates that the cross-linking network in Example 1 dynamically adjusted the porosity during this stage, keeping the error stable at <3.7%.

[0072] During the grain-filling stage (50-70 days), the release rate of 98.1% in Example 1 was almost consistent with the nitrogen requirement of 98%, while the control treatments deviated significantly—Comparative Example 1 released 99.6%, Comparative Example 2 released 99.8%, and Comparative Example 4 released 99.8%, leading to delayed maturity; Comparative Example 3 released 94.8%, which limited grain filling. This indicates that the polyurethane film in Example 1 controlled the release slope at 0.24% / day during this stage, with minimal error compared to the nitrogen requirement slope of 0.28% / day.

[0073] This invention demonstrates that the multilayer structure prepared in this invention achieves precise controlled release through a triple synergistic effect:

[0074] ①The pH-responsive regulation of the basic release rate by the alginate-organic acid acid crosslinking network;

[0075] ② The molten urea layer responds rapidly to the peak nitrogen demand during the seedling stage;

[0076] ③ Bio-based polyurethane membranes achieve linear release in the mid-to-late stages through hydrophobic-hydrophilic microphase separation.

[0077] This spatiotemporal coupling release characteristic makes the nitrogen supply highly compatible with the "less-more-less" nitrogen requirement pattern of corn, fundamentally solving the technical bottleneck of traditional controlled-release fertilizers that are "insufficient in the early stage, excessive in the middle stage, and ineffective in the later stage", and providing experimental support for improving nitrogen fertilizer utilization.

[0078] Experimental Example 2

[0079] 1. Field Trial Design

[0080] To investigate the effect of the controlled-release nitrogen fertilizer containing nitrogen signaling substances prepared in this invention on crop yield, maize was selected as the test crop and field trials were conducted at Shandong Agricultural University. The maize variety used was "Zhengdan 958".

[0081] Each plot in the test area is 20m 2 Six treatments were administered, each repeated four times. Nitrogen fertilizer was applied to the soil simultaneously with maize seeds. Soil composition remained consistent across treatments. Sampling was conducted at the jointing stage (35 days), tasseling stage (60 days), and grain-filling stage (90 days). Maize was harvested after maturity, and grain yield was calculated based on a moisture content of 14%. The results from the field experiment can be expressed as follows: Figure 3 Example 1, Comparative Examples 1-4, plus a blank control, totaling 6 groups of corn yield.

[0082] 2. Microbial community analysis

[0083] Root sampling:

[0084] Take soil samples from the rhizosphere (0-5 mm from the root surface).

[0085] Detection methods: 16S rRNA sequencing (bacterial community); ITS sequencing (fungal community), etc.

[0086] The obtained data results can be expressed as follows: Figure 4 Rhizosphere microbial community analysis in field experiments.

[0087] 3. pH responsiveness verification

[0088] In-situ soil monitoring:

[0089] Three plots with different pH values ​​were selected for bag treatment, with five ion exchange resin bags (20cm deep) buried in each plot.

[0090] Periodic sampling (7, 14, 21, 28, 35, 42, 49, 56, 63, 70 days) to determine the NH4 adsorbed by the resin. + and NO3 - Dynamic changes in rhizosphere soil pH.

[0091] Based on the results measured at the field experiment, it can be expressed as follows: Figure 2 The nitrogen release dynamics of Example 1 in soils with different pH values.

[0092] Configuration and processing:

[0093] Treatment of NPK: Conventional nitrogen, phosphorus and potassium fertilization, application of urea, superphosphate and potassium sulfate (equivalent to 192-60-75 kg of fertilizer per hectare).

[0094] Treatment of NF (Example 1): Apply the controlled-release fertilizer obtained in Example 1, superphosphate, and potassium sulfate (equivalent to N-P2O5-K2O=192-60-75 kg per hectare).

[0095] Treatment of CRU (Comparative Example 1): The controlled-release fertilizer obtained from Comparative Example 1, superphosphate, and potassium sulfate were applied (equivalent to N-P2O5-K2O=192-60-75 kg per hectare).

[0096] Treatment of OA (Comparative Example 2): Apply controlled-release fertilizer obtained from Comparative Example 2, superphosphate, and potassium sulfate (equivalent to N-P2O5-K2O=192-60-75 kg per hectare).

[0097] Treatment AA (Comparative Example 3): The controlled-release fertilizer obtained from Comparative Example 3, superphosphate, and potassium sulfate were applied (equivalent to N-P2O5-K2O=192-60-75 kg per hectare).

[0098] Treatment NW (Comparative Example 4): The controlled-release fertilizer obtained from Comparative Example 4, superphosphate, and potassium sulfate were applied (equivalent to N-P2O5-K2O=192-60-75 kg per hectare).

[0099] Figure 2 The results show that the fertilizer in Example 1 exhibits significant differences in nutrient release in soils with different pH levels:

[0100] Acidic soil (pH 5.2): 99.5% cumulative release rate over 70 days (alginic acid protonation → network swelling → accelerated release);

[0101] Neutral soil (pH 6.8): 70-day cumulative release rate of 98.2% (between acidic and alkaline soils);

[0102] Alkaline soil (pH 8.1): The cumulative release rate after 70 days is only 62.6% (carboxyl dissociation → dense structure → delayed release).

[0103] The above results indicate that the release rate of this controlled-release nitrogen fertilizer is regulated by soil pH: release is accelerated in acidic environments, significantly delayed in alkaline environments, and falls between the two in neutral environments. This demonstrates that the fertilizer of this invention exhibits a clear pH response.

[0104] Maize yield results for each treatment are as follows: Figure 3 As shown, the controlled-release fertilizer obtained in Example 1 promoted maize growth. Compared with the NPK treatment, the NF treatment significantly increased yield by 17.76%; the CRU treatment by 8.47%; the OA treatment by 9.48%; the AA treatment by 12.75%; and the NW treatment by 13.76%. Overall, the application of controlled-release urea containing alginate-organic acid salts significantly increased maize biomass. The controlled-release nitrogen fertilizer containing organic acid salt signaling substances developed in this invention shows significant application potential for significantly increasing maize yield during maize cultivation.

[0105] Rhizosphere microbial community analysis in field trials, such as Figure 4 As shown, the fertilizer of this invention significantly alters the rhizosphere microbial community structure of maize. At the target level ( Figure 4 a) The nitrogen-fixing function in the treatment group of Example 1 Rhizobiales The relative abundance of (Rhizobium) reached 28.5%, showing a significant enrichment trend in all treatment groups; it also inhibited denitrifying bacteria. Burkholderiales (Burkholderia) up to 9.3%, the lowest level among all treatment groups. At the genus level ( Figure 4 b), Example 1: Specific enrichment of growth-promoting bacteria Sphingomonas (Sphingomonas spp., 12.1%) and Pseudomonas(Pseudomonas spp., 15.3%), the relative abundance of both at the genus level was significantly higher in the NPK group and other treatment groups, and they can synergistically promote root development through the secretion of indoleacetic acid. The above changes in the microbial community verified the mechanism described in the above instructions: alginate recruits sphingosine monophosphate (Pseudomonas spp., 15.3%). Sphingomonas ) and organic acid salts synergistically activate the expression of the nifH nitrogen-fixing gene, while Pseudomonas ( Pseudomonas By activating soil insoluble phosphorus through rhizosphere acidification (pH decrease of 0.8 units), the nitrogen fertilizer utilization rate of the treatment group in Example 1 reached 74.7 kg / kg, which was significantly higher than the control group's NPK of 42.1 kg / kg (p<0.01).

[0106] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A controlled-release nitrogen fertilizer containing an organic acid salt signaling substance, characterized in that, From the inside out, the components are urea particles, cross-linked material-trace element mixture, molten urea, and bio-based polyurethane coating material. The crosslinker-trace element mixture is a porous crosslinked material loaded with trace elements; the crosslinker-trace element mixture is obtained by immersing the porous crosslinked material in a solution containing trace elements and then drying it; the trace elements are selected from at least one of zinc, cobalt, molybdenum, and iron. The porous cross-linked material is obtained by cross-linking alginic acid and organic acid salts with a cross-linking agent; The porous cross-linked material is prepared by the following method: Alginic acid was dissolved in deionized water, and the pH was adjusted to 6.5 to obtain an alginic acid solution. An organic acid salt was dissolved in deionized water to obtain an organic acid salt solution. The organic acid salt solution was slowly added to the alginic acid solution while stirring. After stirring until homogeneous, a crosslinking agent solution was added dropwise. The mixture was stirred and reacted at room temperature, and allowed to stand and solidify to form a uniform gel. After filtration, washing, and freeze-drying, a porous crosslinked material was obtained. The crosslinking agent solution contained CaCl2 solution, EDC, and NHS. The organic acid salt was selected from at least one of sodium citrate, sodium fumarate, sodium maleate, and sodium succinate. The controlled-release nitrogen fertilizer containing organic acid salt signaling substances is prepared by the following method: (1) The cross-linked material-trace element mixture is mixed with urea particles and PVA solution is sprayed as an adhesive to make the cross-linked material-trace element mixture uniformly coat the surface of urea particles, thus obtaining urea particles coated with cross-linked material-trace element mixture. (2) Molten urea is atomized and sprayed onto the surface of urea particles to form a dense layer, thereby obtaining coated urea particles; (3) The bio-polyurethane prepolymer is sprayed onto the surface of coated urea particles and cured to obtain controlled-release nitrogen fertilizer containing organic acid salt signaling substances.

2. The controlled-release nitrogen fertilizer containing an organic acid salt signaling substance according to claim 1, characterized in that, The concentration of the alginate solution is 3 wt%; the concentration of the organic acid salt solution is 2-10 wt%; and the molar ratio of the organic acid salt to the alginate is 1:0.5-2.

3. The controlled-release nitrogen fertilizer containing an organic acid salt signaling substance according to claim 1, characterized in that, The concentration of the CaCl2 solution is 2 wt%; the Ca in the CaCl2 solution... 2+ The molar ratio of EDC and NHS is 1:5:2; the Ca in the CaCl2 solution... 2+ With the COO contained in alginic acid - The molar ratio is 3:

10.

4. The controlled-release nitrogen fertilizer containing an organic acid salt signaling substance according to claim 1, characterized in that, The stirring reaction time is 30 min; the static curing time is 12 h; the freeze-drying temperature is -50℃ and the time is 24 h; the pore size of the porous cross-linked material is 50~200 nm.

5. The controlled-release nitrogen fertilizer containing an organic acid salt signaling substance according to claim 1, characterized in that, The solution containing trace elements is selected from at least one of zinc sulfate solution, ferric chloride solution, sodium molybdate solution, and cobalt nitrate solution; the mass ratio of the porous crosslinking material to the trace elements is 10:1; the impregnation pressure is -0.1 MPa and the time is 30 min; the drying is carried out at 60°C until the moisture content is 5%.

6. The controlled-release nitrogen fertilizer containing an organic acid salt signaling substance according to claim 1, characterized in that, The mass ratio of the crosslinker-trace element mixture to urea particles is 1:5; the concentration of the PVA solution is 5wt%; the mass ratio of molten urea to urea particles coated by the crosslinker-trace element mixture is 1:10; the biopolyurethane prepolymer is synthesized from castor oil-based polyol and hexamethylene diisocyanate, and prepared with acetone as a solvent; the mass ratio of the biopolyurethane prepolymer to coated urea particles is 1:

15.

7. The controlled-release nitrogen fertilizer containing an organic acid salt signaling substance as described in any one of claims 1 to 6, in at least one of the following: 1) to 5) 1) Improve nitrogen fertilizer utilization rate; 2) Improve Rhizobiales Relative abundance; 3) Inhibits denitrifying bacteria Burkholderiales; 4) Enrichment of growth-promoting bacteria Sphingomonas and Pseudomonas Relative abundance; 5) Improve pH responsiveness.

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