Preparation method of a tricarboxylic acid chelated compound fertilizer

Abstract

The application discloses a preparation method of a three-acid chelating compound fertilizer, and belongs to the technical field of new-type fertilizers. The three acids include gamma-aminobutyric acid (GABA), polyglutamic acid (PGA) and fulvic acid. The application innovatively adopts a three-step process of "pre-chelation reaction-molecular embedding-low-temperature granulation", first forms pre-chelation complexes of the three acids under specific pH and temperature conditions, then protects the heat-sensitive three acids by a sodium alginate-calcium chloride embedding technology, and finally granulates under a temperature lower than 55 DEG C, thereby solving the technical problem that bioactive substances are prone to inactivation in traditional high-temperature processes. Through the intermolecular synergistic chelation and hierarchical release mechanism of the three acids, the application realizes the synergy of rapid stress resistance response and long-acting nutrient activation, and the phosphorus utilization rate is increased by more than 40%, and is suitable for use in the seedling stage, flowering stage and stress period of crops.

Description

Technical Field

[0001] This invention belongs to the field of novel fertilizer technology, specifically relating to a method for preparing a triacid chelating compound fertilizer. Background Technology

[0002] Phosphorus is an essential macronutrient for plant growth and development, playing a crucial role in physiological processes such as energy metabolism, photosynthesis, and genetic material synthesis. Crops have a particularly high demand for phosphorus during the seedling, flowering, and root development stages. Sufficient phosphorus supply during these stages is crucial for establishing robust root systems, promoting flower bud differentiation, and increasing later-stage yields.

[0003] Currently, high-phosphorus compound fertilizers commonly used in agricultural production (such as the 15-30-5 formula) mainly provide inorganic nutrients, but they have the following technical defects: First, phosphorus is easily fixed in the soil by metal ions such as calcium, magnesium, iron, and aluminum, forming insoluble phosphates, resulting in a phosphorus utilization rate of only 10-25%, causing resource waste and environmental pollution; Second, traditional high-phosphorus compound fertilizers have a single function, only providing mineral nutrients and lacking the biological regulation function for crop root development and stress resistance.

[0004] In recent years, functional fertilizers containing organic acids or bioactive acids have received widespread attention. "Tri-acids" such as γ-aminobutyric acid (GABA, an amino acid), polyglutamic acid (PGA, a polyamino acid), and fulvic acid (a small-molecule humic acid) have been proven to have significant plant physiological regulatory and chelating activation functions. Among them, GABA, as a signaling molecule, can rapidly stimulate plant stress resistance signaling pathways; PGA has extremely strong metal ion chelating ability, and its abundant carboxyl groups can form stable chelates with elements such as phosphorus, calcium, and magnesium in the soil, preventing phosphorus fixation; fulvic acid has good biological activity and permeability, promoting capillary root development and synergistically activating soil nutrients.

[0005] However, existing technologies have significant limitations in combining the aforementioned heat-sensitive "three acids" with compound fertilizers. Traditional compound fertilizer production generally employs high-tower granulation (melting temperature 140-160℃) or rotary drum granulation (steam temperature 100-120℃). GABA begins to decompose above 80℃, PGA undergoes peptide bond breakage and molecular weight degradation under prolonged high temperatures, and the active functional groups in fulvic acid are easily oxidized and deactivated at high temperatures. Therefore, existing technologies typically use these substances as a single foliar fertilizer or add them to finished fertilizers through simple blending. The former increases application costs, while the latter suffers from uneven distribution and poor integration of functional substances with the base fertilizer.

[0006] In summary, how to stably integrate the heat-sensitive "three acids" (GABA, PGA, and fulvic acid) into high-phosphorus compound fertilizers, maintain their biological activity through process innovation, and achieve the integrated function of "nutrient supply + root growth promotion + stress resistance induction + chelation enhancement" is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] The main objective of this invention is to overcome the shortcomings of existing methods for preparing tri-acid chelated compound fertilizers and to provide a new method for preparing tri-acid chelated compound fertilizers. The technical problem to be solved is to innovate a four-step process of "pre-chelation reaction - molecular encapsulation - low-temperature granulation - coating and solidification". First, under specific pH and temperature conditions, the tri-acids form a pre-chelated complex to enhance the synergistic effect. Then, the heat-sensitive tri-acids are microencapsulated and protected using sodium alginate-calcium chloride encapsulation technology. Finally, the tri-acids are released in stages through low-temperature granulation and composite coating. This fundamentally avoids the decomposition and inactivation of the tri-acids at high temperatures and improves the synergistic chelation efficiency and duration of effect of the tri-acids, making it more suitable for practical use and having industrial application value.

[0008] Another objective of this invention is to provide a method for preparing a tri-acid chelating compound fertilizer. The technical problem to be solved is that by controlling the pH of the pre-chelation reaction to 5.5-6.5, the temperature to 20-30℃, the time to 20-40 minutes, and the tri-acid mass ratio to 1:(1.5-2.5):(8-12), hydrogen bonds and coordination bonds are formed between the amino group of GABA and the carboxyl group of PGA and the phenolic hydroxyl group of fulvic acid, thus constructing a tri-acid pre-chelating complex. This significantly enhances the synergistic chelating ability and structural stability of the tri-acids, making it more suitable for practical use.

[0009] Another objective of this invention is to provide a method for preparing a tri-acid chelating compound fertilizer. The technical problem to be solved is to embed the tri-acid pre-chelating compound in calcium alginate microcapsules using a sharp-pore-coagulation bath method, controlling the microcapsule particle size to 0.5-2.0 mm and the embedding rate to 85-95%, thereby achieving effective protection and slow release of the tri-acids. The microcapsules can slowly release the tri-acids in the soil, with a release period of 15-30 days, making it more suitable for practical use.

[0010] Another objective of this invention is to provide a method for preparing a tri-acid chelating compound fertilizer. The technical problem to be solved is that by using a modified paraffin-polyvinyl alcohol composite coating agent with a melting point of 45-55℃ for fluidized bed coating, a coating layer with a thickness of 20-50μm is formed. Together with the internal tri-acid microcapsules, it constitutes a dual protection system of "outer coating-inner microcapsule", realizing the tiered release of tri-acids: the outer coating controls the initial dissolution rate of the fertilizer, and the inner microcapsule controls the slow release rate of tri-acids, thus making it more suitable for practical use.

[0011] The purpose of this invention and the technical problem it solves are achieved by the following technical solution. According to the present invention, a method for preparing a tri-acid chelating compound fertilizer includes the following steps: (1) Pre-chelation reaction: under the conditions of 20-30℃ and pH 5.5-6.5, γ-aminobutyric acid, polyglutamic acid and fulvic acid are dissolved in water at a mass ratio of 1:(1.5-2.5):(8-12), and stirred for 20-40 minutes to form a tri-acid pre-chelating compound aqueous solution; the total mass concentration of the tri-acid is 15-25%; (2) Molecular encapsulation: the tri-acid pre-chelating compound aqueous solution is mixed with sodium alginate solution, and dripped into calcium chloride solution through a sharp-pore-coagulation bath method to form tri-acid microcapsules with a particle size of 0.5-2.0 mm; the mass ratio of sodium alginate to tri-acid is (0.3-0.8):1, and the concentration of calcium chloride solution is 2. -5wt%; (3) Low-temperature granulation: Mix the nitrogen, phosphorus and potassium base fertilizer, the tri-acid microcapsules and the binder, control the material temperature to not exceed 55℃, and make granular fertilizer by extrusion granulation process; the P2O5 content in the nitrogen, phosphorus and potassium base fertilizer accounts for 35-45wt% of the total nutrients, and the mass ratio of N:P2O5:K2O is (13-17):(28-32):(4-6); (4) Coating and curing: Use a modified paraffin-polyvinyl alcohol composite coating agent with a melting point of 45-55℃ to fluidize the granules, and the coating layer thickness is 20-50μm to obtain the finished tri-acid chelated compound fertilizer.

[0012] The objectives of this invention and the technical problems it addresses can be further achieved by the following technical measures.

[0013] In the aforementioned method for preparing triacid chelated compound fertilizer, the pre-chelation reaction in step (1) is carried out at a stirring speed of 200-400 rpm, and nitrogen gas is introduced during the reaction to protect against oxidation.

[0014] In the aforementioned method for preparing triacid chelated compound fertilizer, the mass ratio of γ-aminobutyric acid, polyglutamic acid and fulvic acid in step (1) is 1:2:10.

[0015] In the aforementioned method for preparing triacid chelating compound fertilizer, the mass concentration of sodium alginate solution in step (2) is 3-6%, the diameter of the sharp hole in the sharp hole-coagulation bath method is 0.8-1.5 mm, the temperature of the coagulation bath is 15-25℃, and the drop distance is 5-10 cm.

[0016] The aforementioned method for preparing triacid chelated compound fertilizer, wherein the encapsulation rate of the triacid microcapsules obtained in step (2) is 85-95%, and the slow release time in water at 25°C is 24-72 hours.

[0017] In the aforementioned method for preparing triacid chelated compound fertilizer, the binder in step (3) is a mixture of sodium carboxymethyl cellulose and polyvinylpyrrolidone in a mass ratio of (1-2):1, and the amount of binder added is 2-5% of the total weight of the material.

[0018] In the aforementioned method for preparing triacid chelating compound fertilizer, the extrusion pressure of the extrusion granulation in step (3) is 8-12 MPa, the die temperature is 48-52℃, and the screw speed is 30-60 rpm.

[0019] The aforementioned method for preparing triacid chelated compound fertilizer includes step (3) of which a micronutrient chelate is premixed with nitrogen, phosphorus and potassium base fertilizer. The micronutrient chelate is a mixture of EDTA-Zn, EDTA-Fe, boric acid and citric acid complex, and the amount added is 1.0-3.0 wt% of the total weight of the fertilizer.

[0020] In the aforementioned method for preparing triacid chelated compound fertilizer, in step (4) of the modified paraffin-polyvinyl alcohol composite coating agent, the mass ratio of paraffin to polyvinyl alcohol is (3-5):1, and the amount of coating agent used is 3-6% of the particle weight.

[0021] The objective of this invention and the solution to its technical problems are also achieved by the following technical solution. A tri-acid chelated compound fertilizer according to this invention is prepared by the above-mentioned method. The finished product contains 0.08-0.35 wt% γ-aminobutyric acid, 0.15-0.75 wt% polyglutamic acid, and 1.2-3.5 wt% fulvic acid. The microencapsulated tri-acids have a slow-release period of 15-30 days in the soil.

[0022] The objectives of this invention and the technical problems it addresses can be further achieved by the following technical measures.

[0023] The aforementioned tri-acid chelated compound fertilizer has a particle size of 2.0-4.0 mm and a compressive strength of ≥15 N.

[0024] Compared with the prior art, the present invention has significant advantages and beneficial effects. As can be seen from the above technical solution, in order to achieve the aforementioned objectives, the main technical contents of the present invention are as follows: This invention proposes a method for preparing a tri-acid chelating compound fertilizer. Through a four-step process innovation of "pre-chelation reaction - molecular encapsulation - low-temperature granulation - coating and solidification", a three-level structure of "outer coating - inner microcapsule - core tri-acid pre-chelate" is constructed to achieve synergistic enhancement, effective protection and hierarchical release of the three acids.

[0025] As described above, this invention enables the triacids to form a complex at the molecular level through a pre-chelation reaction, thereby enhancing the synergistic chelation ability; it achieves effective protection of the heat-sensitive triacids through calcium alginate microcapsule encapsulation technology; and it constructs a dual protection system through low-temperature granulation and composite coating, ensuring the activity and sustained-release performance of the triacids.

[0026] By employing the above technical solution, the preparation method of the tri-acid chelating compound fertilizer of the present invention has at least the following advantages: The synergistic effect of the three acids is significantly enhanced: the pre-chelation reaction forms hydrogen bonds and coordination bonds between GABA, PGA and fulvic acid, constructing a stable ternary complex. The synergistic chelation ability is increased by more than 40% compared with simple mixing, and the phosphorus utilization rate is increased by more than 40%. Significant protection effect for heat-sensitive substances: Through dual protection of microencapsulation and low-temperature granulation (<55℃), the activity retention rate of triacids reaches over 95%, which is 50-60 percentage points higher than that of traditional high-temperature processes; Unique tiered release mechanism: outer membrane controls initial release, inner microcapsule enables sustained release, and triacids have a residual effect in soil for 15-30 days, which is 2-3 times longer than unencapsulated products; Outstanding stress resistance and root promotion effects: Field trials show that crops treated with the product of this invention have a more than 60% lower seedling mortality rate under drought stress, a more than 45% increase in root dry weight, and a yield increase of 20-30%. Excellent storage stability: The dual protection of the coating and microcapsule allows the product to be stored at room temperature for 6 months with a loss of less than 5% of the activity of the triacids, which is significantly better than the unprotected product (activity loss >30%).

[0027] In summary, the unique tri-acid chelating compound fertilizer preparation method of this invention, through a combination of pre-chelation reaction, molecular encapsulation, low-temperature granulation, and coating solidification processes, constructs a unique three-level structural system, achieving synergistic enhancement, effective protection, and tiered release of the three acids. It possesses numerous advantages and practical value, and is truly innovative as no similar design has been publicly disclosed or used in similar methods. It represents a significant improvement in both method and function, a substantial technological advancement, and produces user-friendly and practical effects. Furthermore, it offers several enhanced benefits compared to existing tri-acid chelating compound fertilizer preparation methods, making it more suitable for practical application and possessing broad industrial applicability. It is indeed a novel, progressive, and practical new design.

[0028] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0029] The specific method of the present invention is given in detail in the following embodiments and accompanying drawings. Attached Figure Description

[0030] Figure 1 The graph shows the effect of different temperature treatments on the retention rate of triacid activity. Detailed Implementation

[0031] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following detailed description, in conjunction with the accompanying drawings and preferred embodiments, describes the specific implementation methods, steps, structures, features, and effects of the preparation method of the tri-acid chelating compound fertilizer proposed according to the present invention.

[0032] The preferred embodiment of the preparation method of the tri-acid chelating compound fertilizer of the present invention mainly includes the following steps: Step (1): Pre-chelation reaction At 20-30℃ and pH 5.5-6.5, γ-aminobutyric acid, polyglutamic acid, and fulvic acid are dissolved in water at a mass ratio of 1:(1.5-2.5):(8-12). The mixture is stirred at 200-400 rpm for 20-40 minutes, with nitrogen gas introduced for protection during the reaction, to form an aqueous solution of the tri-acid prechelated complex; the total mass concentration of the tri-acid is 15-25%.

[0033] Step (2): Molecular embedding The aqueous solution of the triacid prechelated complex was mixed with a sodium alginate solution of 3-6% by mass, and then dropped into a calcium chloride solution of 2-5 wt% by sharp-pore coagulation bath method to form triacid microcapsules with a particle size of 0.5-2.0 mm. The mass ratio of sodium alginate to triacid was (0.3-0.8):1, the diameter of the sharp pore was 0.8-1.5 mm, the coagulation bath temperature was 15-25℃, and the drop distance was 5-10 cm. The encapsulation efficiency of the obtained triacid microcapsules was 85-95%, and the slow release time in water at 25℃ was 24-72 hours.

[0034] Step (3): Low-temperature granulation The nitrogen, phosphorus, and potassium basic fertilizer, the tri-acid microcapsules, and the binder are mixed, and the material temperature is controlled to not exceed 55℃. The mixture is then extruded and granulated to produce granular fertilizer. The nitrogen, phosphorus, and potassium basic fertilizer contains 35-45 wt% P2O5 of the total nutrients, and the mass ratio of N:P2O5:K2O is (13-17):(28-32):(4-6). The binder is a mixture of sodium carboxymethyl cellulose and polyvinylpyrrolidone, with a mass ratio of (1-2):1. The amount of binder added is 2-5% of the total weight of the material. The extrusion pressure for the granulation process is 8-12 MPa, the die temperature is 48-52℃, and the screw speed is 30-60 rpm.

[0035] Step (4): Coating curing The particles are coated in a fluidized bed using a modified paraffin-polyvinyl alcohol composite coating agent with a melting point of 45-55℃. The coating layer thickness is 20-50μm, resulting in a tri-acid chelating compound fertilizer product. In the modified paraffin-polyvinyl alcohol composite coating agent, the mass ratio of paraffin to polyvinyl alcohol is (3-5):1, and the amount of coating agent used is 3-6% of the particle weight.

[0036] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to these embodiments. Example

[0037] A method for preparing a tri-acid chelating compound fertilizer includes the following steps: Step (1): Pre-chelation reaction At 25℃ and pH 6.0, 3 kg of γ-aminobutyric acid (99% purity, food grade), 6 kg of polyglutamic acid (molecular weight 150 kDa, content 90%, produced by bio-fermentation), and 30 kg of fulvic acid (80% fulvic acid content, mineral-derived) were added to 150 kg of deionized water. Under nitrogen protection, the reaction was carried out at 300 rpm for 30 minutes to form an aqueous solution of a tri-acid prechelated complex with a total tri-acid mass concentration of 26%. pH changes during the reaction were monitored using potentiometric titration to ensure the reaction system remained stable within the pH range of 5.8-6.2.

[0038] Step (2): Molecular embedding The above-mentioned triacid prechelated complex aqueous solution was mixed evenly with 40 kg of 5% sodium alginate solution (2 kg sodium alginate, viscosity 200±20 mPa·s). The mixture was then dropped dropwise through a 1.0 mm diameter sharp orifice into a 3 wt% calcium chloride solution at 25 °C at a drop distance of 8 cm. After solidification for 30 minutes, the mixture was filtered and washed to obtain triacid microcapsules with a particle size of 1.0-1.5 mm. High-performance liquid chromatography (HPLC) analysis showed that the triacid encapsulation rate was 92%, and the sustained-release time in water at 25 °C was 48 hours.

[0039] Step (3): Low-temperature granulation 250 kg of urea (N 46%, particle size ≤0.5 mm), 650 kg of monoammonium phosphate (N 11%, P2O5 44%, particle size ≤0.5 mm), and 100 kg of potassium sulfate (K2O 50%, particle size ≤0.5 mm) were pulverized and passed through a 40-mesh sieve. Then, 10 kg of EDTA-Zn (Zn 15%), 5 kg of EDTA-Fe (Fe 13%), and 5 kg of boric acid-citric acid complex (B 10%) were added and mixed thoroughly to obtain the basic fertilizer. The above-mentioned tri-acid microcapsules and 20 kg of binder (sodium carboxymethyl cellulose: polyvinylpyrrolidone = 1.5:1) were added, and the moisture content of the material was controlled at 10-12%. Granulation was performed using a twin-screw extruder at an extrusion pressure of 10 MPa, a die temperature of 50℃, and a screw speed of 45 rpm to obtain cylindrical wet granules with a particle size of 2.5-3.5 mm.

[0040] Step (4): Coating curing A modified paraffin-polyvinyl alcohol composite coating agent with a melting point of 50℃ (paraffin:polyvinyl alcohol = 4:1, polyvinyl alcohol degree of hydrolysis 88%) was used at a dosage of 4% of the particle weight. Coating was carried out in a fluidized bed coating machine with the inlet air temperature controlled at 45-48℃ and the coating time at 15 minutes. The coating layer thickness was 30-40μm, resulting in a tri-acid chelating compound fertilizer product.

[0041] Product Specifications: The resulting product, N-P2O5-K2O, has a particle size of 15-30-5 and contains 0.18 wt% γ-aminobutyric acid, 0.36 wt% polyglutamic acid, 1.8 wt% fulvic acid, 0.15% Zn, 0.065% Fe, and 0.05% B. The particle size is 2.0-4.0 mm, the compressive strength is 22 N, the microcapsule encapsulation rate is 92%, and the triacid activity retention rate is 96.5%. Example

[0042] A method for preparing a tri-acid chelating compound fertilizer includes the following steps: Step (1): Pre-chelation reaction At 22℃ and pH 5.8, 4 kg of γ-aminobutyric acid, 8 kg of polyglutamic acid (molecular weight 120 kDa) and 40 kg of fulvic acid were added to 200 kg of deionized water. Under nitrogen protection, the mixture was stirred at 250 rpm for 35 minutes, and the total mass concentration of the three acids was 26%.

[0043] Step (2): Molecular embedding Mixed with 50 kg of 4% sodium alginate solution (2 kg of sodium alginate), the mixture was dripped into a 3.5 wt% calcium chloride solution through a 1.2 mm diameter sharp orifice. The coagulation bath temperature was 20 °C, the drop distance was 10 cm, and the mixture was solidified for 25 minutes to obtain microcapsules with a particle size of 1.2-1.8 mm, an encapsulation rate of 89%, and a slow release time of 36 hours in water at 25 °C.

[0044] Step (3): Low-temperature granulation The basic fertilizer formula consists of 220 kg urea, 680 kg monoammonium phosphate, 80 kg potassium chloride (K2O 60%), 15 kg EDTA-Zn, 8 kg EDTA-Fe, 8 kg boric acid-citric acid complex, and 25 kg binder (sodium carboxymethyl cellulose: polyvinylpyrrolidone = 2:1). The extrusion pressure is 12 MPa, the die temperature is 48℃, and the screw speed is 40 rpm.

[0045] Step (4): Coating curing Modified paraffin-polyvinyl alcohol coating agent (ratio 3:1), dosage 5%, melting point 48℃, coating layer thickness 40-50μm.

[0046] Product Specifications: The resulting product, N-P2O5-K2O, has a particle size of 14-32-5 and contains 0.22 wt% γ-aminobutyric acid, 0.44 wt% polyglutamic acid, 2.2 wt% fulvic acid, 0.225% Zn, 0.104% Fe, and 0.08% B. The particles have a compressive strength of 25 N and retain 95.8% of the tri-acid activity. Example

[0047] A method for preparing a tri-acid chelating compound fertilizer includes the following steps: Step (1): Pre-chelation reaction At 28℃ and pH 6.2, 2 kg of γ-aminobutyric acid, 4 kg of polyglutamic acid (molecular weight 180 kDa) and 20 kg of fulvic acid were added to 100 kg of deionized water. Under nitrogen protection, the mixture was stirred at 350 rpm for 25 minutes, and the total mass concentration of the three acids was 26%.

[0048] Step (2): Molecular embedding Mixed with 25 kg of 6% sodium alginate solution (1.5 kg of sodium alginate), the mixture was dripped into 2 wt% calcium chloride solution through a 0.8 mm diameter sharp hole. The coagulation bath temperature was 18 °C, the drop distance was 6 cm, and the mixture was solidified for 35 minutes to obtain microcapsules with a particle size of 0.8-1.2 mm, an encapsulation rate of 94%, and a slow release time of 60 hours in water at 25 °C.

[0049] Step (3): Low-temperature granulation The basic fertilizer formula consists of 280 kg urea, 600 kg monoammonium phosphate, and 120 kg potassium sulfate, with the addition of 8 kg EDTA-Zn, 4 kg EDTA-Fe, 3 kg boric acid-citric acid complex, and 15 kg binder (sodium carboxymethyl cellulose: polyvinylpyrrolidone = 1:1). The extrusion pressure is 8 MPa, the die temperature is 52℃, and the screw speed is 50 rpm.

[0050] Step (4): Coating curing Modified paraffin-polyvinyl alcohol coating agent (ratio 5:1), dosage 3%, melting point 52℃, coating layer thickness 20-30μm.

[0051] Product Specifications: The resulting product, N-P2O5-K2O, has a composition of 16-28-6 and contains 0.12 wt% γ-aminobutyric acid, 0.24 wt% polyglutamic acid, and 1.2 wt% fulvic acid. The particle compressive strength is 18 N, and the tri-acid activity retention rate is 97.1%.

[0052] Comparative Example 1: A method for preparing a tri-acid chelating compound fertilizer differs from Example 1 in that: Step (1): Simple Mixing At 25°C, 3 kg of γ-aminobutyric acid, 6 kg of polyglutamic acid and 30 kg of fulvic acid were simply mixed and dissolved in 150 kg of deionized water and stirred for 10 minutes without pre-chelation reaction or nitrogen protection.

[0053] The remaining steps (2)-(4) are the same as in Example 1.

[0054] Product Specifications: The resulting product had a tri-acid encapsulation rate of 85% and a particle compressive strength of 20 N. Infrared spectroscopy analysis showed that no obvious hydrogen bonds or coordination bonds were formed between the three acids, and the copper ion chelating ability was reduced by 42% compared to Example 1.

[0055] Comparative Example 2: A method for preparing a tri-acid chelating compound fertilizer differs from Example 1 in that: The molecular encapsulation process in step (2) is omitted, and the aqueous solution of the tri-acid prechelate complex in step (1) is directly sprayed into the basic fertilizer for low-temperature granulation.

[0056] The remaining steps are the same as in Example 1.

[0057] Product Specifications: The obtained product retained 78% of the tri-acid activity (after 30 days of storage), a decrease of 18.5 percentage points compared to Example 1. Soil column leaching tests showed that 82% of the tri-acid was released within 3 days, significantly shortening the effective period.

[0058] Comparative Example 3: A method for preparing a tri-acid chelating compound fertilizer differs from Example 1 in that: Step (3): High-temperature granulation The traditional rotary drum granulation process is adopted, with a steam temperature of 120℃ and a material temperature of 110-130℃. After granulation, a rotary dryer is used for drying, with a hot air temperature of 150℃.

[0059] The remaining steps (1), (2), and (4) are the same as in Example 1.

[0060] Product Specifications: The resulting product retained only 38% of the activity of the three acids, had a GABA decomposition rate of 62%, PGA molecular weight degraded to below 50 kDa, and the phenolic hydroxyl content of fulvic acid decreased by 45%. Field trials showed that the fertilizer efficiency was reduced by more than 55% compared to Example 1.

[0061] Application effect test: To verify the technical effectiveness of the tri-acid chelating compound fertilizer prepared by the method of this invention, the following field trials were conducted: Experiment 1: Determination of the synergistic chelating ability of three acids The chelating ability of the products in each example was determined by copper ion chelation titration (GB / T 21884-2008):

[0062] The results showed that the pre-chelation reaction significantly enhanced the synergistic chelation ability of the three acids, with a 42.1% reduction in Example 4 compared to Example 1, demonstrating the necessity of the pre-chelation step.

[0063] Experiment 2: Thermal stability comparison test The products of each embodiment were stored in a 60°C constant temperature oven for 30 days to determine the retention rate of triacid activity.

[0064] The results showed that microencapsulation and low-temperature processing were crucial for the protection of the activity of the triacids, with Example 1 showing a 51.9 percentage point improvement over Example 6.

[0065] Experiment 3: Determination of slow-release performance (soil column leaching test) An acrylic column with a diameter of 5 cm and a height of 30 cm was filled with air-dried soil (passed through a 2 mm sieve) to a height of 25 cm. Glass fiber cotton and a 200-mesh nylon mesh were placed at the bottom of the soil column. 2.0 g of each example product was evenly spread on the surface of the soil column. Distilled water was added dropwise from the top using a peristaltic pump at a flow rate of 1 mL / min. The leachate was collected every 24 hours, and the cumulative release rate of the triacids was determined.

[0066] The results showed that Examples 1-3 had ideal sustained-release properties, Example 5 released too quickly due to the lack of microcapsule encapsulation, and Example 6 released irregularly due to the destruction of the triacid structure caused by high temperature.

[0067] Experiment 4: Field test on root-promoting effect Experimental Location: Modern Agricultural High-tech Integration Demonstration Park, Shouguang City, Shandong Province. Crop: Tomato (Variety: Jinpeng No. 1, seedling trays). Soil Type: Loam, organic matter content 18.5 g / kg, available phosphorus 45.2 mg / kg, pH 7.2. Experimental Design: Seven treatments were set up: (1) Product of Example 1, (2) Product of Example 2, (3) Product of Example 4, (4) Product of Example 5, (5) Product of Example 6, (6) Conventional 15-30-5 compound fertilizer (high tower granulation), (7) Blank control (no fertilizer). Each treatment was replicated 3 times, arranged in a randomized block design, with a plot area of ​​20 m². The application rate was 40 kg per mu, applied as basal fertilizer before transplanting.

[0068] Root indicators were measured 20 days after tomato transplanting (pre-flowering stage):

[0069] The results showed that the root dry weight of Example 1 increased by 87.1% compared with conventional compound fertilizer and by 48.7% compared with Example 6, demonstrating the synergistic contribution of pre-chelation reaction, microencapsulation and low temperature process to the root-promoting effect.

[0070] Experiment 5: Field stress resistance test Experimental Location: Dryland Agriculture Experimental Station, Yuyang District, Yulin City, Shaanxi Province. Crop: Maize (Variety: Zhengdan 958). Soil Type: Yellow Loess, Organic Matter Content 8.6 g / kg, Available Phosphorus 12.5 mg / kg, pH 8.1. Experimental Design: Three treatments were set up: (1) Product of Example 1, (2) Conventional 15-30-5 Compound Fertilizer, (3) Blank Control. Each treatment was replicated 3 times, arranged in a randomized block design, with a plot area of ​​50 m². The application rate was 50 kg per mu, applied as basal fertilizer before sowing.

[0071] During the corn seedling stage (3-leaf stage), a 15-day drought stress treatment (natural rainfall + rain shelter) was applied, and the seedling mortality rate and related physiological indicators were investigated.

[0072] The results showed that Example 1 reduced the seedling mortality rate by 66.5% and increased the yield by 26.3% compared with conventional compound fertilizer, demonstrating significant stress resistance and yield increase effects.

[0073] Experiment 6: Phosphorus Utilization Rate Experiment Using ³²P isotope tracing technology, the utilization rate of phosphorus fertilizer by tomatoes was determined under pot conditions (pot diameter 20cm, height 25cm, soil content 5kg):

[0074] The results showed that the phosphorus utilization rate of Example 1 was 68.4% higher than that of conventional compound fertilizer and 43.8% higher than that of Example 6, demonstrating the significant effect of pre-chelation reaction and low-temperature process on improving phosphorus utilization.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the methods and techniques disclosed above without departing from the scope of the present invention to create equivalent embodiments. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a tri-acid chelating compound fertilizer, characterized in that, Includes the following steps: (1) Pre-chelation reaction: Under the conditions of 20-30℃ and pH 5.5-6.5, γ-aminobutyric acid, polyglutamic acid and fulvic acid are dissolved in water at a mass ratio of 1:(1.5-2.5):(8-12), and the mixture is stirred for 20-40 minutes to form an aqueous solution of the tri-acid pre-chelation complex; the total mass concentration of the tri-acid is 15-25%; (2) Molecular encapsulation: The aqueous solution of the triacid prechelated complex is mixed with a sodium alginate solution and then dripped into a calcium chloride solution using a sharp-pore coagulation bath method to form triacid microcapsules with a particle size of 0.5-2.0 mm; the mass ratio of sodium alginate to triacid is (0.3-0.8):1, and the concentration of calcium chloride solution is 2-5 wt%. (3) Low-temperature granulation: The nitrogen, phosphorus and potassium basic fertilizer, the tri-acid microcapsules and the binder are mixed, and the material temperature is controlled not to exceed 55℃. The granules are made by extrusion granulation process; the P2O5 content in the nitrogen, phosphorus and potassium basic fertilizer accounts for 35-45wt% of the total nutrients, and the mass ratio of N:P2O5:K2O is (13-17):(28-32):(4-6); (4) Coating and curing: The particles are coated in a fluidized bed using a modified paraffin polyvinyl alcohol composite coating agent with a melting point of 45-55℃. The coating layer thickness is 20-50μm, and the finished product of tri-acid chelating compound fertilizer is obtained.

2. The preparation method according to claim 1, characterized in that, The pre-chelation reaction described in step (1) is carried out at a stirring speed of 200-400 rpm, and nitrogen gas is introduced during the reaction to protect against oxidation.

3. The preparation method according to claim 1, characterized in that, The mass ratio of γ-aminobutyric acid, polyglutamic acid and fulvic acid in step (1) is 1:2:

10.

4. The preparation method according to claim 1, characterized in that, The sodium alginate solution in step (2) has a mass concentration of 3-6%, the diameter of the sharp hole in the sharp hole coagulation bath method is 0.8-1.5 mm, the coagulation bath temperature is 15-25℃, and the drop distance is 5-10 cm.

5. The preparation method according to claim 1, characterized in that, The encapsulation rate of the triacid microcapsules obtained in step (2) is 85-95%, and the sustained release time in water at 25°C is 24-72 hours.

6. The preparation method according to claim 1, characterized in that, The binder mentioned in step (3) is a mixture of sodium carboxymethyl cellulose and polyvinylpyrrolidone in a mass ratio of (1-2):1, and the amount of binder added is 2-5% of the total weight of the material.

7. The preparation method according to claim 1, characterized in that, The extrusion pressure of the extrusion granulation in step (3) is 8-12 MPa, the die temperature is 48-52℃, and the screw speed is 30-60 rpm.

8. The preparation method according to claim 1, characterized in that, Step (3) also includes a step of pre-mixing the micronutrient chelate with the nitrogen, phosphorus and potassium base fertilizer. The micronutrient chelate is a mixture of EDTA-Zn, EDTA-Fe, boric acid and citric acid complex, and the amount added is 1.0-3.0 wt% of the total weight of the fertilizer.

9. The preparation method according to claim 1, characterized in that, In step (4), the mass ratio of paraffin to polyvinyl alcohol in the modified paraffin-polyvinyl alcohol composite coating agent is (3-5):1, and the amount of coating agent used is 3-6% of the particle weight.

10. The triacid chelating compound fertilizer prepared by the preparation method according to any one of claims 1-9, characterized in that, The finished product contains 0.08-0.35 wt% γ-aminobutyric acid, 0.15-0.75 wt% polyglutamic acid, and 1.2-3.5 wt% fulvic acid. The microcapsule-encapsulated triacids have a slow-release period of 15-30 days in the soil.

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