Preparation method of humic acid-containing water-soluble organic fertilizer with synergistic effect of trace elements in chelation

Abstract

The present application relates to the field of organic fertilizer manufacturing, in particular to a preparation method of a chelated humic acid-containing water-soluble organic fertilizer with synergistic microelement, the preparation steps are as follows: step S1: adding modified humic acid into deionized water, heating to 40-50 DEG C, stirring for 25-35 min, adding ferrous sulfate hydrate, passing compressed air, stirring for 30-50 min, etc.; the present application improves the environmental adaptability of humic acid through molecular structure modification, constructs a composite chelating system to enhance element stability, optimizes the multi-stage chelating sequence to prevent ion antagonism, and innovates the physical barrier to realize intelligent controlled release of the core process path, compared with the prior art, the present application effectively breaks through the functional limitations of traditional fertilizers in complex agricultural ecological systems, significantly improves the nutrient utilization efficiency and agronomic sustainability, and has a broad application prospect in soil remediation, precision agriculture and resource-saving planting system.

Description

Technical Field

[0001] This invention relates to the field of organic fertilizer manufacturing, and more particularly to a method for preparing humic acid-containing water-soluble organic fertilizer that chelates and enhances the effects of trace elements. Background Technology

[0002] Water-soluble organic fertilizers refer to a type of organic fertilizer derived from plants, animals, or microorganisms. Through physical, chemical, and biological processes, their main nutrient components can be completely dissolved in water to form a stable solution. By combining the advantages of organic fertilizers with modern efficient fertilization technologies, precise, efficient, and convenient application of organic nutrients can be achieved. They are mainly used in drip irrigation, sprinkler irrigation, micro-sprinkler irrigation fertilization, and soilless cultivation in organic agriculture.

[0003] In existing technologies, when water-soluble fertilizers containing humic acid are applied in saline-alkali land or hard water irrigation areas, the conventional humic acid is prone to flocculation and sedimentation in environments with pH > 7.5, leading to a significant reduction in the bioavailability of micronutrients. Simultaneously, key elements such as iron and zinc exhibit strong antagonism in the complex chelate system due to competition for binding sites, causing nutrient imbalance in crops. Furthermore, traditional formulations lack slow-release design, resulting in leaching within 48 hours under irrigation conditions, leading to the loss of effective components, especially in sandy soils. Although existing technologies attempt to improve performance using synthetic chelating agents or physical coatings, they face new problems: chelating agents lose their binding ability with calcium and magnesium ions in hard water, leading to decreased stability and difficulty in biodegradation.

[0004] Therefore, based on the relevant technologies mentioned above, there is an urgent need to develop a formula for preparing humic acid-containing water-soluble organic fertilizer that chelates trace elements to enhance their effects. Summary of the Invention

[0005] In view of this, the purpose of this invention is to propose a method for preparing humic acid-containing water-soluble organic fertilizer that chelates and enhances the effects of trace elements, in order to solve the problems of poor environmental adaptability of humic acid and severe element antagonism in the prior art.

[0006] To achieve the above objectives, this invention provides a method for preparing humic acid-containing water-soluble organic fertilizer that chelates and enhances the effects of trace elements.

[0007] A method for preparing a humic acid-containing water-soluble organic fertilizer with chelated trace elements, characterized by the following preparation steps:

[0008] Step S1: Add modified humic acid to deionized water, heat to 40-50℃, stir for 25-35 minutes, add hydrated ferrous sulfate, introduce compressed air, stir and react for 30-50 minutes to obtain chelate solution;

[0009] Step S2: Add the modified chelating agent and citric acid to the chelation solution, heat to 40-50℃, stir for 8-12 min, add hydrated zinc sulfate, hydrated manganese sulfate and boric acid, stir for 15-20 min, add 10% ammonia solution, adjust pH to 5-6, stir reaction for 50-70 min at 250-350 rpm to obtain composite chelation solution;

[0010] Step S3: Add urea to the compound chelation solution, heat to 30-40℃, stir for 10-20 min, add potassium dihydrogen phosphate and potassium sulfate, stir for 18-22 min at 250-350 rpm, continue stirring for 10-20 min to obtain nutrient chelation mother liquor.

[0011] Step S4: Add the nutrient chelation mother liquor to the concentration tank, reduce the pressure to -0.08MPa, raise the temperature to 40-50℃, compress for 50-70min, add nano silica and modified starch, stir for 8-12min, add to the high-pressure homogenizer, process for 5-7min at a pressure of 23-27MPa, filter, dry, cool, and pass through an 80-mesh vibrating sieve to obtain water-soluble organic fertilizer;

[0012] Because Fe 3+ Humic acid readily hydrolyzes into a colloidal precipitate at pH > 4, while in an acidic environment of pH 2.5-3.5, the carboxyl and phenolic hydroxyl groups of humic acid preferentially react with Fe. 3+ A stable five-membered ring chelate is formed, thus preventing its transformation into a precipitate. Simultaneously, as pH increases, Zn... 2+ / Mn 2+ By binding with the o-hydroxyphenylacetic acid group of the modified chelating agent, distribution chelation and elemental synergistic anti-antagonism are achieved.

[0013] Preferably, the mass ratio of modified humic acid to hydrated ferrous sulfate in step S1 is 2.7-2.8:1;

[0014] The mass ratio of the modified chelating agent, citric acid, chelating solution, hydrated zinc sulfate, hydrated manganese sulfate and boric acid in step S2 is 0.016-0.018:0.008-0.009:1:0.008-0.009:0.0045-0.0055:0.003-0.004.

[0015] Preferably, the mass ratio of urea, compound chelate, potassium dihydrogen phosphate and potassium sulfate in step S3 is 0.05-0.052:1:0.032-0.034:0.024-0.026.

[0016] Preferably, the mass ratio of the nutrient chelating mother liquor, nano-silica, and modified starch in step S4 is 1:0.008-0.012:0.028-0.032.

[0017] Preferably, the preparation steps of the modified humic acid are as follows:

[0018] Step A1: Add weathered coal powder to a 1.5% potassium hydroxide solution, heat to 60-80℃, stir for 80-100 min, centrifuge for 10-20 min at 3000-5000 rpm to obtain activated humic acid solution;

[0019] Step A2: Under a nitrogen atmosphere, aminosulfonic acid and 37% formaldehyde solution are added to the activated humic acid solution, 10% sodium hydroxide solution is added, the pH is adjusted to 9.0-10.0, the temperature is raised to 80-90℃, and the reaction is stirred for 100-140 min. After the reaction is complete, the temperature is lowered to 40-60℃, 10% hydrochloric acid solution is added, the pH is adjusted to 2.0-3.0, the precipitate is allowed to stand, centrifuged and washed, and dried to obtain modified humic acid.

[0020] A sulfonic acid group is introduced into the humic acid molecule via an aminosulfonic acid-formaldehyde condensation reaction. The sulfonic acid group is a strong acid group that can completely ionize to -SO3 in the pH range of 0-14. - This forms a permanent hydrophilic layer, thereby increasing the negative charge density on the molecular surface. The electrostatic repulsion prevents aggregation and precipitation. At the same time, the sulfonic acid group forms a bidentate chelate structure with the original carboxyl group, which can increase the number of chelation sites.

[0021] Preferably, the mass ratio of weathered coal powder to 1.5% potassium hydroxide solution in step A1 is 1:7.8-8.2;

[0022] The mass ratio of aminosulfonic acid, 37% formaldehyde solution and activated humic acid solution in step A2 is 0.026-0.028:0.0065-0.007:1.

[0023] Preferably, the modified chelating agent is prepared using the following steps:

[0024] Ethylenediamine di-o-hydroxyphenylacetic acid and sodium polyaspartate were added to deionized water, heated to 43-47℃, stirred for 30-40 min, and the catalyst carbodiimide hydrochloride was added. 0.1 mol / L hydrochloric acid solution was added to adjust the pH to 5.8-6.2, and the temperature was raised to 48-52℃. The reaction was stirred for 2-4 h at a speed of 200-300 rpm. After the reaction was completed, the temperature was lowered to 20-30℃, purified, freeze-dried, pulverized and sieved to obtain the modified chelating agent.

[0025] Sodium polyaspartate molecules contain densely packed carboxyl groups, which can react with Ca in hard water. 2+ / Mg 2+ The formation of a soluble complex consumes interfering ions and reduces interference from other ions on ethylenediamine di-o-hydroxyphenylacetic acid. Simultaneously, iron in ethylenediamine di-o-hydroxyphenylacetic acid reacts with Ca... 2+ At that time, sodium polyaspartate-Ca 2+The complex preemptively binds to free Ca via entropy-driven substitution. 2+ This blocks its competition for the coordination site of ethylenediamine di-o-hydroxyphenylacetic acid, while simultaneously blocking the ortho-phenolic hydroxyl group -O of ethylenediamine di-o-hydroxyphenylacetic acid. - With carboxyl-COO - Forming a rigid octahedral coordination cavity, with Fe 3+ The charge / radius ratio is perfectly matched, thereby reducing Fe 3+ The degree of dissociation; furthermore, the long chain of sodium polyaspartate is branched to the outside of the benzene ring of ethylenediamine di-o-hydroxyphenylacetic acid, and its hydrophobic carbon chain physically blocks Ca. 2+ It is located near the active site of ferric di-o-hydroxyphenylacetate in ethylenediamine.

[0026] Preferably, the mass ratio of ethylenediamine di-o-hydroxyphenylacetic acid, sodium polyaspartate, and catalyst is 1:1.4-1.6:0.18-0.22.

[0027] Preferably, the preparation steps of the modified starch are as follows:

[0028] Add cassava starch to deionized water, heat to 20-30℃, stir for 10-20 min, add 3% sodium hydroxide solution, adjust pH to 8-9, heat to 33-37℃, add octenyl succinic anhydride, react for 160-200 min, after the reaction is complete, add 10% hydrochloric acid solution, adjust pH to 6.3-6.7, cool and let stand, centrifuge and wash, dry and pulverize to obtain modified starch;

[0029] By directionally arranging the octenyl long chains, the octenyl hydrophobic chains can be anchored to the starch molecular backbone, forming a dense hydrophobic layer. This reduces the water molecule permeation rate and delays the dissolution of internal nutrients. Simultaneously, when the modified starch comes into contact with water, the hydrophilic region absorbs water and swells moderately, but the hydrophobic chain network restricts unlimited swelling, preventing the capsule wall from rupturing. Furthermore, the nanoscale capillaries formed by swelling bind nutrients through surface tension, causing them to be released slowly. In addition, the carboxyl groups ionize in alkaline soil, and the electrostatic repulsion expands the capillary pore size, accelerating the release; under acidic conditions, the pore size shrinks, achieving intelligent response.

[0030] Preferably, the mass ratio of cassava starch to octenyl succinic anhydride is 1:0.07-0.09.

[0031] The beneficial effects of this invention are:

[0032] This invention provides a method for preparing humic acid-containing water-soluble organic fertilizer with enhanced efficiency through chelation of trace elements. The core process pathway of this invention is to improve the environmental adaptability of humic acid through molecular structure modification, enhance element stability by constructing a composite chelation system, optimize multi-level chelation sequence to prevent ion antagonism, and innovate physical barriers to achieve intelligent controlled release. Compared with existing technologies, this invention effectively breaks through the functional limitations of traditional fertilizers in complex agricultural ecosystems, significantly improves nutrient utilization efficiency and agronomic sustainability, and has broad application prospects in soil remediation, precision agriculture, and resource-saving planting systems. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0034] Example 1: The preparation steps of modified humic acid are as follows:

[0035] S1: Add 100g of weathered coal powder to 780g of 1.5% potassium hydroxide solution, heat to 60℃, stir for 100min, centrifuge for 10min at 5000rpm to obtain activated humic acid solution.

[0036] S2: Under a nitrogen atmosphere, 2.6 g of aminosulfonic acid and 0.65 g of 37% formaldehyde solution were added to 100 g of activated humic acid solution. 10% sodium hydroxide solution was added to adjust the pH to 9.0-10.0. The temperature was raised to 80℃ and the reaction was stirred for 140 min. After the reaction was completed, the temperature was lowered to 40℃, 10% hydrochloric acid solution was added, and the pH was adjusted to 2.0-3.0. The mixture was allowed to stand to precipitate, centrifuged, washed, and dried to obtain modified humic acid.

[0037] Example 2: The preparation steps of modified humic acid are as follows:

[0038] S1: Add 100g of weathered coal powder to 800g of 1.5% potassium hydroxide solution, heat to 70℃, stir for 90min, centrifuge for 15min at 4000rpm to obtain activated humic acid solution.

[0039] S2: Under a nitrogen atmosphere, 2.7g of aminosulfonic acid and 0.68g of 37% formaldehyde solution were added to 100g of activated humic acid solution. 10% sodium hydroxide solution was added to adjust the pH to 9.0-10.0. The temperature was raised to 85℃ and the reaction was stirred for 120min. After the reaction was completed, the temperature was lowered to 50℃, 10% hydrochloric acid solution was added, and the pH was adjusted to 2.0-3.0. The mixture was allowed to stand to precipitate, centrifuged, washed, and dried to obtain modified humic acid.

[0040] Example 3: The preparation steps of modified humic acid are as follows:

[0041] S1: Add 100g of weathered coal powder to 820g of 1.5% potassium hydroxide solution, heat to 80℃, stir for 80min, centrifuge for 20min at 3000rpm to obtain activated humic acid solution.

[0042] S2: Under a nitrogen atmosphere, 2.8 g of aminosulfonic acid and 0.7 g of 37% formaldehyde solution were added to 100 g of activated humic acid solution. 10% sodium hydroxide solution was added to adjust the pH to 9.0-10.0. The temperature was raised to 90℃ and the reaction was stirred for 100 min. After the reaction was completed, the temperature was lowered to 60℃, 10% hydrochloric acid solution was added, and the pH was adjusted to 2.0-3.0. The mixture was allowed to stand to precipitate, centrifuged, washed, and dried to obtain modified humic acid.

[0043] Example 4: The preparation steps of the modified chelating agent are as follows:

[0044] 100g of ethylenediamine di-o-hydroxyphenylacetic acid and 140g of sodium polyaspartate were added to 500mL of deionized water. The mixture was heated to 43℃ and stirred for 40min. 18g of carbodiimide hydrochloride catalyst was added, followed by 0.1mol / L hydrochloric acid solution. The pH was adjusted to 5.8-6.2, and the mixture was heated to 48℃ and stirred for 4h at 200rpm. After the reaction was complete, the mixture was cooled to 20℃, purified, freeze-dried, pulverized, and sieved to obtain the modified chelating agent.

[0045] Example 5: The preparation steps of the modified chelating agent are as follows:

[0046] 100g of ethylenediamine di-o-hydroxyphenylacetic acid and 150g of sodium polyaspartate were added to 500mL of deionized water. The mixture was heated to 45℃ and stirred for 35min. 20g of carbodiimide hydrochloride catalyst was added, followed by 0.1mol / L hydrochloric acid solution. The pH was adjusted to 5.8-6.2. The mixture was heated to 50℃ and stirred for 3h at 250rpm. After the reaction was complete, the mixture was cooled to 25℃, purified, freeze-dried, pulverized, and sieved to obtain the modified chelating agent.

[0047] Example 6: The preparation steps of the modified chelating agent are as follows:

[0048] 100g of ethylenediamine di-o-hydroxyphenylacetic acid and 160g of sodium polyaspartate were added to 500mL of deionized water. The mixture was heated to 47℃ and stirred for 30min. 22g of the catalyst carbodiimide hydrochloride was added, followed by 0.1mol / L hydrochloric acid solution. The pH was adjusted to 5.8-6.2, and the mixture was heated to 52℃ and stirred for 2h at 300rpm. After the reaction was complete, the mixture was cooled to 20℃, purified, freeze-dried, pulverized, and sieved to obtain the modified chelating agent.

[0049] Example 7: The preparation steps of the modified starch are as follows:

[0050] Add 100g of cassava starch to 200mL of deionized water, heat to 20℃, stir for 20min, add 3% sodium hydroxide solution, adjust pH to 8-9, heat to 33℃, add 7g of octenyl succinic anhydride, react for 200min, after the reaction is complete, add 10% hydrochloric acid solution, adjust pH to 6.3-6.7, cool and let stand, centrifuge, wash, dry and pulverize to obtain modified starch.

[0051] Example 8: The preparation steps of the modified starch are as follows:

[0052] Add 100g of cassava starch to 200mL of deionized water, heat to 25℃, stir for 15min, add 3% sodium hydroxide solution, adjust pH to 8-9, heat to 35℃, add 8g of octenyl succinic anhydride, react for 180min, after the reaction is complete, add 10% hydrochloric acid solution, adjust pH to 6.3-6.7, cool and let stand, centrifuge, wash, dry and pulverize to obtain modified starch.

[0053] Example 9: The preparation steps of the modified starch are as follows:

[0054] Add 100g of cassava starch to 200mL of deionized water, heat to 30℃, stir for 10min, add 3% sodium hydroxide solution, adjust pH to 8-9, heat to 37℃, add 9g of octenyl succinic anhydride, react for 160min, after the reaction is complete, add 10% hydrochloric acid solution, adjust pH to 6.3-6.7, cool and let stand, centrifuge, wash, dry and pulverize to obtain modified starch.

[0055] Example 10: Preparation method of humic acid-containing water-soluble organic fertilizer with chelated trace elements for enhanced efficacy:

[0056] S1: Add 270g of modified humic acid to 500mL of deionized water, heat to 40℃, stir for 35min, add 100g of hydrated ferrous sulfate, introduce compressed air, stir and react for 30min to obtain chelate solution.

[0057] S2: Add 1.6g of modified chelating agent and 0.8g of citric acid to 100g of chelating solution, heat to 40℃, stir for 12min, add 0.8g of hydrated zinc sulfate, 0.45g of hydrated manganese sulfate and 0.3g of boric acid, stir for 15min, add 10% ammonia solution, adjust pH to 5-6, stir reaction for 70min at 250rpm to obtain composite chelating solution;

[0058] S3: Add 5g of urea to 100g of compound chelation solution, heat to 30℃, stir for 20min, add 3.2g of potassium dihydrogen phosphate and 2.4g of potassium sulfate, stir for 18min at 350rpm, continue stirring for 10min to obtain nutrient chelation mother liquor.

[0059] S4: Add 100g of nutrient chelation mother liquor to a concentration tank, reduce the pressure to -0.08MPa, raise the temperature to 40℃, compress for 70min, add 0.8g of nano silica and 2.8g of modified starch, stir for 8min, add to a high-pressure homogenizer, process for 7min at a pressure of 23MPa, filter, dry, cool, and pass through an 80-mesh vibrating sieve to obtain water-soluble organic fertilizer.

[0060] Example 11: Preparation method of humic acid-containing water-soluble organic fertilizer with chelated trace elements for enhanced efficacy:

[0061] S1: Add 275g of modified humic acid to 500mL of deionized water, heat to 45℃, stir for 30min, add 100g of hydrated ferrous sulfate, introduce compressed air, stir and react for 40min to obtain chelate solution.

[0062] S2: Add 1.7g of modified chelating agent and 0.85g of citric acid to 100g of chelating solution, heat to 45℃, stir for 10min, add 0.85g of hydrated zinc sulfate, 0.5g of hydrated manganese sulfate and 0.35g of boric acid, stir for 18min, add 10% ammonia solution, adjust pH to 5-6, stir reaction for 60min at 300rpm to obtain composite chelating solution;

[0063] S3: Add 5.1g of urea to 100g of compound chelation solution, heat to 35℃, stir for 15min, add 3.3g of potassium dihydrogen phosphate and 2.5g of potassium sulfate, stir for 20min at 300rpm, and continue stirring for 15min to obtain nutrient chelation mother liquor.

[0064] S4: Add 100g of nutrient chelation mother liquor to a concentration tank, reduce the pressure to -0.08MPa, raise the temperature to 45℃, compress for 60min, add 0.1g of nano silica and 3g of modified starch, stir for 10min, add to a high-pressure homogenizer, process for 6min at a pressure of 25MPa, filter, dry, cool, and pass through an 80-mesh vibrating sieve to obtain water-soluble organic fertilizer.

[0065] Example 12: Preparation method of humic acid-containing water-soluble organic fertilizer with chelated trace elements for enhanced efficacy:

[0066] S1: Add 280g of modified humic acid to 500mL of deionized water, heat to 50℃, stir for 25min, add 100g of hydrated ferrous sulfate, introduce compressed air, stir and react for 50min to obtain chelate solution.

[0067] S2: Add 1.8g of modified chelating agent and 0.9g of citric acid to 100g of chelating solution, heat to 50℃, stir for 8min, add 0.9g of hydrated zinc sulfate, 0.55g of hydrated manganese sulfate and 0.4g of boric acid, stir for 20min, add 10% ammonia solution, adjust pH to 5-6, stir reaction for 50min at 350rpm to obtain composite chelating solution;

[0068] S3: Add 5.2g of urea to 100g of compound chelation solution, heat to 40℃, stir for 10min, add 3.4g of potassium dihydrogen phosphate and 2.6g of potassium sulfate, stir for 22min at 250rpm, and continue stirring for 20min to obtain nutrient chelation mother liquor.

[0069] S4: Add 100g of nutrient chelation mother liquor to a concentration tank, reduce the pressure to -0.08MPa, raise the temperature to 50℃, compress for 50min, add 1.2g of nano silica and 3.2g of modified starch, stir for 12min, add to a high-pressure homogenizer, process for 5min at a pressure of 27MPa, filter, dry, cool, and pass through an 80-mesh vibrating sieve to obtain water-soluble organic fertilizer.

[0070] Comparative Example 1:

[0071] Compared with Example 10, this comparative example directly adds all raw materials in the preparation process of water-soluble organic fertilizer, and the remaining steps and parameters are the same. This comparative example will not be repeated here. Finally, water-soluble organic fertilizer is obtained.

[0072] Comparative Example 2:

[0073] This comparative example differs from Example 10 only in that "modified humic acid" is replaced with "humic acid". All other steps and parameters are the same, and will not be repeated here. The final result is a water-soluble organic fertilizer.

[0074] Comparative Example 3:

[0075] Compared with Example 10, this comparative example did not add nano-silica and modified starch in the preparation process of water-soluble organic fertilizer. All other steps and parameters were the same, and will not be repeated here. The final result was water-soluble organic fertilizer.

[0076] Comparative Example 4:

[0077] Compared with Example 10, this comparative example only replaces the "modified chelating agent" with "ethylenediaminetetraacetic acid chelating agent". All other steps and parameters are the same, and will not be repeated in this comparative example. Finally, water-soluble organic fertilizer is obtained.

[0078] Performance testing:

[0079] Humic acid and alkaline stability test:

[0080] According to the testing standard GB / T35107-2017 "Water-soluble humic acid fertilizer", a Shimadzu UV-2600 spectrophotometer was used.

[0081] 1. Experimental Group: Take 1.0 g of each of the water-soluble organic fertilizers from Examples 10-12 and Comparative Examples 1-4, add them to 100 mL of boric acid buffer solution with pH=8.5, heat to 25℃, shake for 24 h, centrifuge, filter the supernatant, and measure the absorbance at 465 nm, denoted as A. t ;

[0082] 2. Control group: Take 1.0g of water-soluble organic fertilizer from Examples 10-12 and Comparative Examples 1-4 respectively, add 100mL of deionized water, centrifuge and filter, measure absorbance at 465nm and record it as A0;

[0083] 3. Calculation of residual rate: A t Absorbance after 24 hours, A o Initial absorbance.

[0084] Table 1

[0085] project <![CDATA[A t ]]> <![CDATA[A0]]> Humic acid residue rate (%) Example 10 0.486 0.495 98.2 Example 11 0.483 0.494 97.8 Example 12 0.488 0.496 98.4 Comparative Example 1 0.205 0.496 41.3 Comparative Example 2 0.226 0.495 45.7 Comparative Example 3 0.479 0.495 96.8 Comparative Example 4 0.472 0.494 95.5

[0086] Hard water chelation stability test:

[0087] According to the HG / T5331-2018 "Testing Standard for Trace Elements in Water-Soluble Fertilizers", an inductively coupled plasma atomic emission spectrometer was used.

[0088] 1. Preparation of hard water: Add 0.368g of anhydrous calcium chloride and 0.228g of hydrated magnesium chloride to 1000mL of deionized water, stir to dissolve, and obtain hard water;

[0089] 2. Take 0.5g of each of the water-soluble organic fertilizers from Examples 10-12 and Comparative Examples 1-4, add 100mL of hard water, gently shake to disperse, heat to 40℃, shake at 150rpm, react for 120min, filter, separate, and obtain the filtrate.

[0090] 3. Take 10 ml of the filtrate and dilute it with deionized water to 50 mL, then determine the concentrations of free iron and zinc;

[0091] 4. Calculate the degree of chelation: .

[0092] Table 2

[0093] project Chelation rate (iron) (%) Chelation rate (zinc) (%) Example 10 96.5 95.8 Example 11 95.7 96.1 Example 12 96.2 95.3 Comparative Example 1 52.3 58.6 Comparative Example 2 94.1 93.7 Comparative Example 3 95.0 94.5 Comparative Example 4 63.8 67.2

[0094] Sustained-release performance test:

[0095] Referring to the testing standard of NY / T 1977-2010 "Slow-Release Fertilizers", dialysis bags with a molecular weight cutoff of 8000 Da were used;

[0096] 1. Take 1.0g of each of the water-soluble organic fertilizers from Examples 10-12 and Comparative Examples 1-4, put them into a dialysis bag, add 200mL of deionized water, heat to 25℃, shake at 100rpm for 72h to obtain the external solution.

[0097] 2. Take 10 mL of the external solution, determine the amount of nutrients dissolved, and calculate the cumulative release rate R. t (%) , M t : Cumulative dissolution amount at time point t, M 总 m: The theoretical total content of this nutrient in the sample loaded in the dialysis bag; W: Mass fraction of this nutrient in the sample.

[0098] Table 3

[0099] project <![CDATA[M 72h (mg)]]> <![CDATA[M 总 (mg)]]> <![CDATA[R t (%)]]> Example 10 49.3 100.0 49.3 Example 11 51.2 100.0 51.2 Example 12 48.7 100.0 48.7 Comparative Example 1 89.1 100.0 89.1 Comparative Example 2 52.8 100.0 52.8 Comparative Example 3 92.6 100.0 92.6 Comparative Example 4 87.9 100.0 87.9

[0100] Crop absorption efficiency test:

[0101] The Thermo Fisher iCE3500 atomic absorption spectrometer was used in accordance with the ISO 18644:2016 standard for evaluating the bioavailability of trace elements in fertilizers.

[0102] 1. Soil pretreatment: Take calcareous soil, heat it to 105℃, dry it for 48 hours to sterilize it, cool it, pack it into pots of 5 kg each, and compact it to a bulk density of 1.3 g / cm³. 3 ;

[0103] 2. Experimental group: Take water-soluble organic fertilizer from Examples 10-12 and Comparative Examples 1-4 respectively, apply 1.2g of fertilizer to each pot, and cover with 1cm of soil after basal application;

[0104] Control group: Take an equal amount of conventional fertilizer with the same nutrients, the formula of which is urea, potassium dihydrogen phosphate, potassium sulfate and EDTA-Fe / Zn. Apply 1.2g of fertilizer per pot and cover with 1cm of soil after basal application.

[0105] Blank group: No fertilizer applied.

[0106] 3. Sow 5 corn seeds in each pot, and retain 3 strong seedlings after emergence. Cultivation conditions: 25±1℃, 16h light, 60%±5% humidity, maintain soil moisture content of 60% WHC, and cultivate for 30 days.

[0107] 4. Take the third fully expanded leaf, rinse with deionized water, heat to 105℃, fix for 30 minutes, cool to 70℃, dry, pulverize and sieve, weigh 0.2g, add 5mL concentrated nitric acid, microwave digest, make up to 25mL, filter and test.

[0108] 5. Data Calculation: Nutrient Content: Absorption gain rate:

[0109] Table 4

[0110] project <![CDATA[C Fe (mg / kg)]]> <![CDATA[Gain Fe (%)]]> <![CDATA[C zn (mg / kg)]]> <![CDATA[Gain zn (%)]]> Example 10 142.6 82.4 58.3 90.2 Example 11 144.9 85.1 51.8 88.7 Example 12 140.9 80.6 59.1 91.5 Comparative Example 1 78.5 15.3 59.1 19.8 Comparative Example 2 86.7 28.7 32.1 86.4 Comparative Example 3 138.2 76.5 57.5 87.9 Comparative Example 4 92.4 35.6 41.7 483

[0111] Data Analysis:

[0112] As can be seen from Tables 1-4, the humic acid-containing water-soluble organic fertilizer with chelated trace element enhancement prepared by the present invention has better nutrient slow release, anti-ion antagonism ability and crop absorption efficiency.

[0113] In contrast, Comparative Example 1, due to the direct mixing of all raw materials, resulted in strong antagonism between iron and zinc ions in an alkaline environment. This was because Fe... 3+ At pH > 4, Zn preferentially hydrolyzes to form colloidal precipitates, blocking the chelation sites of humic acid; simultaneously... 2+ with Fe 3+ Competitive chelation ligands reduce the bioavailability of both, and the stepwise chelation process uses pH gradient control to directionally bind Fe to the carboxyl groups of humic acid. 3+ It forms a five-membered ring chelate, preventing precipitation and transformation at the source;

[0114] Comparative Example 2 showed that replacing modified humic acid with humic acid caused flocculation and sedimentation in soil with pH 8.2. This was because the carboxyl group of conventional humic acid had a sharp drop in ionization in an alkaline environment. Intermolecular hydrogen bonds and π-π stacking led to an increase in particle size to the micrometer level, which encapsulated trace elements and caused them to precipitate together. Meanwhile, the modified humic acid, through sulfonic acid grafting, maintained a strong ionization state in the pH range of 0-14. The electrostatic repulsion caused the Zeta potential to drop from -15mV to -38mV, effectively inhibiting aggregation.

[0115] Comparative Example 3, due to the absence of nano-SiO2 and modified starch, achieved a leaching rate of 92% in 72 hours. This was because the fertilizer granules lacked a physical barrier, allowing water to directly penetrate and dissolve nutrients. Meanwhile, the octenyl long chains of the modified starch formed a dense hydrophobic layer, which bound nutrient molecules through the pressure generated by the nanocapillaries. Furthermore, the nano-SiO2 filled the pores, reducing the swelling rate and synergistically extending the release period to 240 hours.

[0116] Comparative Example 4 showed a 76% decrease in zinc chelation stability in hard water due to the replacement of the modified chelating agent with ethylenediaminetetraacetic acid (EDTA). This was because EDTA reacts with Ca... 2+ The binding constant is much higher than that of Zn. 2+ Calcium ions competitively occupy coordination sites, and the carboxyl clusters of sodium polyaspartate in the modified chelating agent preferentially bind to Ca. 2+ It forms a soluble complex, blocking calcium interference through an entropy-driven effect; furthermore, the rigid octahedral cavity of ethylenediamine di-o-hydroxyphenylacetic acid interacts with Zn. 2+ A perfect match, achieving specific chelation protection.

[0117] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

[0118] This invention is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for preparing humic acid-containing water-soluble organic fertilizer with chelated trace elements for enhanced efficacy, characterized in that, The preparation steps are as follows: Step S1: Add modified humic acid to deionized water, heat to 40-50℃, stir for 25-35 minutes, add hydrated ferrous sulfate, introduce compressed air, stir and react for 30-50 minutes to obtain chelate solution; Step S2: Add the modified chelating agent and citric acid to the chelation solution, heat to 40-50℃, stir for 8-12 min, add hydrated zinc sulfate, hydrated manganese sulfate and boric acid, stir for 15-20 min, add 10% ammonia solution, adjust pH to 5-6, stir reaction for 50-70 min at 250-350 rpm to obtain composite chelation solution; Step S3: Add urea to the compound chelation solution, heat to 30-40℃, stir for 10-20 min, add potassium dihydrogen phosphate and potassium sulfate, stir for 18-22 min at 250-350 rpm, continue stirring for 10-20 min to obtain nutrient chelation mother liquor. Step S4: Add the nutrient chelation mother liquor to the concentration tank, reduce the pressure to -0.08MPa, raise the temperature to 40-50℃, compress for 50-70min, add nano silica and modified starch, stir for 8-12min, add to the high-pressure homogenizer, process for 5-7min at a pressure of 23-27MPa, filter, dry, cool, and pass through an 80-mesh vibrating sieve to obtain water-soluble organic fertilizer; The mass ratio of modified humic acid to hydrated ferrous sulfate in step S1 is 2.7-2.8:1; The mass ratio of the modified chelating agent, citric acid, chelating solution, hydrated zinc sulfate, hydrated manganese sulfate, and boric acid in step S2 is 0.016-0.018:0.008-0.009:1:0.008-0.009:0.0045-0.0055:0.003-0.004; In step S3, the mass ratio of urea, compound chelating solution, potassium dihydrogen phosphate, and potassium sulfate is 0.05-0.052:1:0.032-0.034:0.024-0.

026. The mass ratio of the nutrient chelation mother liquor, nano-silica, and modified starch in step S4 is 1:0.008-0.012:0.028-0.032; The preparation steps of the modified humic acid are as follows: Step A1: Add weathered coal powder to a 1.5% potassium hydroxide solution, heat to 60-80℃, stir for 80-100 min, centrifuge for 10-20 min at 3000-5000 rpm to obtain activated humic acid solution; Step A2: Under a nitrogen atmosphere, aminosulfonic acid and 37% formaldehyde solution are added to the activated humic acid solution, 10% sodium hydroxide solution is added, the pH is adjusted to 9.0-10.0, the temperature is raised to 80-90℃, and the reaction is stirred for 100-140 min. After the reaction is complete, the temperature is lowered to 40-60℃, 10% hydrochloric acid solution is added, the pH is adjusted to 2.0-3.0, the precipitate is allowed to stand, centrifuged and washed, and dried to obtain modified humic acid. The modified chelating agent is prepared in the following steps: Ethylenediamine di-o-hydroxyphenylacetic acid and sodium polyaspartate were added to deionized water, heated to 43-47℃, stirred for 30-40 min, and the catalyst carbodiimide hydrochloride was added. 0.1 mol / L hydrochloric acid solution was added to adjust the pH to 5.8-6.2, and the temperature was raised to 48-52℃. The reaction was stirred for 2-4 h at a speed of 200-300 rpm. After the reaction was completed, the temperature was lowered to 20-30℃, purified, freeze-dried, pulverized and sieved to obtain the modified chelating agent. The preparation steps of the modified starch are as follows: Add cassava starch to deionized water, heat to 20-30℃, stir for 10-20 minutes, add 3% sodium hydroxide solution, adjust pH to 8-9, heat to 33-37℃, add octenyl succinic anhydride, react for 160-200 minutes, after the reaction is complete, add 10% hydrochloric acid solution, adjust pH to 6.3-6.7, cool and let stand, centrifuge, wash, dry and pulverize to obtain modified starch.

2. The method for preparing humic acid-containing water-soluble organic fertilizer with chelated trace element enhancement according to claim 1, characterized in that, The mass ratio of weathered coal powder to 1.5% potassium hydroxide solution in step A1 is 1:7.8-8.2; The mass ratio of aminosulfonic acid, 37% formaldehyde solution and activated humic acid solution in step A2 is 0.026-0.028:0.0065-0.007:

1.

3. The method for preparing humic acid-containing water-soluble organic fertilizer with chelated trace element enhancement according to claim 1, characterized in that, The mass ratio of ethylenediamine di-o-hydroxyphenylacetic acid, sodium polyaspartate, and catalyst is 1:1.4-1.6:0.18-0.

22.

4. The method for preparing humic acid-containing water-soluble organic fertilizer with chelated trace element enhancement according to claim 1, characterized in that, The mass ratio of cassava starch to octenyl succinic anhydride is 1:0.07-0.09.