Humic acid-containing value-added fertilizer for activating soil insoluble phosphorus and preparation method thereof

Abstract

The application discloses a humic acid-containing value-added fertilizer for activating soil insoluble phosphorus and a preparation method thereof, and belongs to the technical field of agricultural fertilizers. The fertilizer contains, in terms of weight fractions, 5-30 parts of activated humic acid, 3-20 parts of phosphatized modified humic acid, 50-90 parts of phosphate ammonium and 1-10 parts of activation aids. The application firstly performs physical-chemical synergic activation treatment on humic acid raw materials to obtain activated humic acid; then performs gradient temperature grafting modification on part of the activated humic acid under the assistance of an ultrasonic field and with a phosphatizing agent to obtain phosphatized modified humic acid; and then mixes the activated humic acid, the modified humic acid and the phosphate ammonium to form the fertilizer. The application significantly increases the content of active functional groups of the humic acid through physical-chemical synergic activation, significantly improves the grafting rate and water solubility of phosphate groups through ultrasonic field assistance-gradient temperature grafting modification, and realizes multi-path activation of soil insoluble phosphorus through the synergic effect of the three components.

Description

Technical Field

[0001] This invention relates to the field of agricultural fertilizer technology, and more specifically to a humic acid-containing value-added fertilizer for activating insoluble phosphorus in soil and its preparation method. Background Technology

[0002] Phosphorus is one of the three essential nutrients for crop growth and development, playing an irreplaceable role in physiological processes such as energy metabolism, nucleic acid synthesis, and cell membrane structure maintenance. However, after phosphate fertilizer is applied to the soil, most of the phosphorus (approximately 70%–90%) is rapidly fixed by calcium, iron, and aluminum ions in the soil, forming insoluble phosphates, leading to a sharp decline in phosphorus availability. This phosphorus fixation effect typically results in a utilization rate of only 10%–25% for phosphate fertilizer in the current season, with large amounts of phosphorus accumulating in the soil in an insoluble state. This not only causes a huge waste of phosphate rock resources but also poses a risk of agricultural non-point source pollution. Therefore, how to activate the fixed insoluble phosphorus in the soil and improve phosphorus availability has always been a hot topic and a challenge in the field of agricultural fertilizers.

[0003] Humic acid, as an important component of soil organic matter, possesses abundant active functional groups such as carboxyl, phenolic hydroxyl, and quinone groups. It can interact with metal ions in the soil through various mechanisms, including complexation, chelation, and ion exchange, thereby releasing fixed phosphate ions. Existing technologies have widely disclosed the ability of humic acid to activate insoluble phosphorus in the soil. The patent application (CN103274798A) filed in 2013 by the Institute of Agricultural Resources and Regional Planning of the Chinese Academy of Agricultural Sciences, entitled "A Humic Acid-Enhanced Ammonium Phosphate and Its Preparation Method," uses humic acid as the main raw material to prepare an enhancing carrier, which is then combined with ordinary ammonium phosphate to produce humic acid-enhanced ammonium phosphate products. This process slows down the fixation of phosphorus in the soil while simultaneously activating phosphorus in the soil. Furthermore, other patents disclose a technical solution involving high-energy mechanical grinding of phosphate rock to enhance its chemical activity through mechanochemical activation, followed by granulation after adding humic acid to the premix and undergoing high-energy activation treatment.

[0004] In recent years, researchers have begun to focus on the chemical modification of humic acid to enhance its functional properties. Existing patents disclose technical solutions for phosphorylation modification using humic acid as a raw material. For example, CN118307363B discloses an organic fertilizer containing a phosphorylated humic acid synergistic carrier and its preparation method, achieving phosphorylation modification and value enhancement of humic acid nutrients. Phosphorylated humic acid has better solubility, thus promoting the synergistic effect of phosphate fertilizer. Another patent (CN109320364A) discloses a method for preparing a modified phosphoric acid-containing liquid fertilizer, which involves a phosphorylation esterification reaction of humate salts and a phosphorylation reagent in an acidic aqueous system, cleaving the long carbon chains of humic acid molecules and performing graft modification.

[0005] However, existing technologies still have the following shortcomings: First, the activation effect of humic acid is unstable and is affected by various factors such as the source of humic acid, activation method, and application conditions, making it difficult to guarantee continuous and efficient activation performance.

[0006] Second, the activation pathways for humic acid in existing technologies are relatively simple, either using only physical activation (such as mechanical grinding) or only chemical activation (such as acid-base treatment). A single activation pathway is insufficient to fully stimulate the active functional groups of humic acid, resulting in limited activation efficiency.

[0007] Third, existing humic acid phosphorylation modification technologies mainly employ traditional heating and stirring reaction methods. This results in low grafting efficiency between the phosphorylation reagent and humic acid molecules, low grafting rates of phosphate groups, and poor grafting uniformity, thus affecting the functional performance of the modified humic acid. Traditional phosphorylation modification is typically carried out at a constant temperature, lacking a staged temperature control strategy, making it difficult to achieve selective grafting of the phosphorylation reagent onto different active sites of the humic acid molecule.

[0008] Fourth, in existing humic acid value-added fertilizers, the humic acid components are relatively simple and lack the synergistic combination of different functional humic acid components, making it difficult to achieve synergistic activation effects through multiple pathways and mechanisms.

[0009] In summary, the existing technology lacks a humic acid-containing value-added fertilizer and its preparation method that can simultaneously solve the technical problems of unstable humic acid activation effect, low efficiency of single activation pathway, insufficient grafting rate and uniformity of phosphorylation grafting modification, and lack of synergistic effect of single humic acid components.

[0010] Therefore, how to effectively improve the activation efficiency of humic acid for insoluble phosphorus in soil, while ensuring the stability of product performance and the diversity of activation pathways, and achieving synergistic effects among different functional humic acid components, is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0011] One object of the present invention is to provide a humic acid-containing value-added fertilizer for activating insoluble phosphorus in soil. This fertilizer significantly improves the activation efficiency of humic acid for insoluble phosphorus in soil through the organic combination of physical-chemical synergistic activation and ultrasonic-assisted gradient temperature grafting modification.

[0012] Another objective of this invention is to provide a method for preparing the above-mentioned humic acid-containing value-added fertilizer and its application, which is simple in process and suitable for industrial production.

[0013] To achieve the above objectives, this application adopts the following technical solution: The primary objective of this application is to provide a humic acid-containing value-added fertilizer for activating insoluble phosphorus in soil, comprising the following components by weight: 5-30 parts activated humic acid, 3-20 parts phosphoric acid modified humic acid, 50-90 parts ammonium phosphate, and 1-10 parts activation adjuvant.

[0014] As a preferred technical solution, the activated humic acid is prepared by physical-chemical synergistic activation treatment of humic acid raw materials. The specific activation process is as follows: after pulverizing the humic acid raw materials, a chemical activator is added, and ball milling activation is carried out in a ball mill. During the ball milling process, the mechanical force causes the humic acid particles to be continuously pulverized and refined, the specific surface area increases significantly, the crystal structure is distorted, and the internal energy increases; at the same time, the chemical activator, with the assistance of mechanical force, penetrates and infiltrates more fully into the interior of the humic acid particles, reacting with the active groups in the humic acid molecules, further increasing the number of active sites in the humic acid molecules for complexing and chelating fixed ions such as calcium, iron, and aluminum in the soil.

[0015] As a preferred technical solution, the chemical activator is selected from one or more of potassium hydroxide, sodium carbonate, and ammonia water, and the amount of chemical activator added is 0.5% to 10% of the mass of the humic acid raw material. The above-mentioned alkaline activator can effectively break the hydrogen bonds and van der Waals forces between humic acid molecules, promote the loosening and dissociation of the humic acid macromolecular structure, and expose more active functional groups; simultaneously, the cations (K+) in the activator... + Na + NH4 + It can undergo ion exchange reactions with the carboxyl and phenolic hydroxyl groups in humic acid, converting humic acid into more water-soluble humate salts, further enhancing its reactivity. Controlling the amount of activator added within the range of 0.5% to 10% ensures sufficient activation—too low an amount results in insufficient activation and inadequate exposure of functional groups; too high an amount may lead to excessive degradation of humic acid and destruction of active functional groups.

[0016] As a preferred technical solution, the phosphorylated modified humic acid is prepared by grafting the aforementioned activated humic acid with a phosphorylating reagent under ultrasonic field assistance through a gradient temperature increase modification reaction. The phosphorylating reagent is selected from one or more of phosphoric acid, phosphate, and polyphosphoric acid. The ultrasonic power of the ultrasonic field assistance is 100-500W, and the ultrasonic frequency is 20-80kHz. By introducing the synergistic effect of ultrasonic field assistance and phosphorylating reagent, the phosphorylation grafting efficiency of humic acid is significantly improved. The shock wave, microjets, and reactive oxygen free radicals generated by the ultrasonic cavitation effect effectively break the aggregation state of humic acid molecules, promoting the penetration and diffusion of phosphorylating reagent into the molecule; on the other hand, it causes moderate oxidative degradation of humic acid molecules, exposing more active reaction sites and providing sufficient reaction opportunities for the grafting of phosphate groups.

[0017] As a preferred technical solution, the gradient temperature grafting modification reaction includes the following steps: activating humic acid and phosphorylation reagent are mixed at a mass ratio of 100:1 to 100:20, and the grafting reaction is carried out under ultrasonic field assistance according to a gradient temperature program: the first stage is carried out at 40 to 70°C for 0.5 to 2 hours, the second stage is carried out at 70 to 100°C for 1 to 3 hours, and the third stage is carried out at 100 to 150°C for 0.5 to 2 hours to obtain phosphorylated modified humic acid.

[0018] By combining a gradient-temperature grafting strategy with ultrasonic field assistance, ordered and efficient grafting of phosphate groups onto different active sites of humic acid molecules was achieved. Specifically: the first stage, a low-temperature range (40–70°C), favors the preferential grafting of phosphorylation reagents onto the most reactive phenolic and alcoholic hydroxyl groups on the surface of humic acid molecules. The low temperature effectively controls the reaction rate and avoids localized oversaturation of grafting. The second stage, a medium-temperature range (70–100°C), allows the phosphorylation reagents to penetrate into the humic acid molecules and graft onto active groups such as carboxyl and quinone groups. This stage is the main stage of the grafting reaction, where most phosphate groups are grafted. The third stage, a high-temperature range (100–150°C), further activates the relatively inert deep active sites in the molecule and promotes the expulsion of water generated in the reaction, shifting the grafting equilibrium towards the product and improving the completion of the grafting reaction. The combined effect of the three-stage gradient temperature increase and the physical fragmentation and mass transfer enhancement caused by the cavitation effect of the ultrasonic field results in a significantly higher grafting rate and water solubility of phosphate groups compared to traditional isothermal modification methods.

[0019] As a preferred technical solution, the ammonium phosphate is selected from one or two of monoammonium phosphate and diammonium phosphate; the activating agent is selected from one or more of zeolite powder, ammonium citrate, and polyglutamic acid.

[0020] Another object of this application is to provide: a method for preparing the above-mentioned humic acid-containing value-added fertilizer, comprising the following steps: (1) Physical-chemical synergistic activation treatment of humic acid raw materials to obtain activated humic acid; (2) The activated humic acid obtained in step (1) is subjected to gradient temperature grafting modification with phosphorylation reagent under the assistance of ultrasonic field to obtain phosphorylated modified humic acid. (3) Mix the activated humic acid obtained in step (1), the phosphorylated modified humic acid obtained in step (2), ammonium phosphate and the activation aid in a certain proportion; (4) The mixture obtained in step (3) is processed into the humic acid-containing value-added fertilizer.

[0021] As a preferred technical solution, the physical-chemical synergistic activation treatment in step (1) includes: crushing the humic acid raw material through a 40-100 mesh sieve, adding a chemical activator, and ball milling and activating it in a ball mill; The chemical activator is selected from one or more of potassium hydroxide, sodium carbonate, and ammonia water, and the amount of chemical activator added is 0.5% to 10% of the mass of humic acid raw material.

[0022] As a preferred technical solution, the ultrasonic field-assisted gradient heating grafting modification in step (2) is carried out under a protective atmosphere, which is selected from nitrogen and argon. By carrying out grafting modification under a protective atmosphere, the oxidative side reaction of oxygen on humic acid molecules and phosphorylation reagents during the high-temperature reaction is effectively avoided. Specifically, nitrogen or argon, as an inert protective gas, can remove oxygen and moisture from the reaction system, preventing the oxidation and failure of active functional groups in humic acid molecules and the decomposition or deterioration of phosphorylation reagents under high-temperature conditions (especially in the third stage at 100–150°C), thus ensuring the directionality of the grafting reaction and the chemical stability of the modified product. Simultaneously, the protective atmosphere also helps suppress side reactions in the reaction system, ensuring that phosphate groups are selectively grafted onto the target active sites of humic acid molecules. The specific modification process is as follows: activated humic acid and phosphorylation reagent are mixed at a mass ratio of 100:1 to 100:20. Under the assistance of an ultrasonic field with an ultrasonic power of 100–500W and an ultrasonic frequency of 20–80kHz, the grafting reaction is carried out according to a gradient temperature program: the first stage is at 40–70°C for 0.5–2 hours, the second stage is at 70–100°C for 1–3 hours, and the third stage is at 100–150°C for 0.5–2 hours. The phosphorylation reagent is selected from one or more of phosphoric acid, phosphate, and polyphosphoric acid.

[0023] Another object of this application is to provide the application of the above-mentioned humic acid-containing value-added fertilizer or the humic acid-containing value-added fertilizer prepared by the above method, wherein the application is in any of the following directions: (1) Activate insoluble phosphorus in the soil; (2) Increase the available phosphorus content in the soil; (3) Promotes the absorption of phosphorus by crops and / or promotes crop growth.

[0024] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: (1) Physicochemical synergistic activation significantly enhances humic acid activity This invention combines mechanical chemical activation with chemical activators for humic acid raw materials. During ball milling, mechanical force refines humic acid particles, increases their specific surface area, and distorts their crystal structure; the chemical activator, aided by mechanical force, fully penetrates and reacts with active groups, increasing the number of functional groups such as carboxyl and phenolic hydroxyl groups. The two activation pathways work synergistically, increasing the total acidic group content by 69.4% compared to unactivated humic acid, far superior to single physical activation (22.1%) or single chemical activation (31.6%).

[0025] (2) Achieving efficient phosphorylation through ultrasonic field-assisted gradient temperature grafting modification This invention introduces ultrasonic field assistance into the phosphorylation modification of humic acid. The ultrasonic cavitation effect generates shock waves and microjets, breaking up the aggregation of humic acid molecules and promoting the inward penetration and diffusion of phosphorylation reagents; the active free radicals generated by cavitation moderately oxidize and degrade humic acid, exposing more reaction sites; the ultrasonic mechanical effect continuously renews the reaction interface, ensuring uniform grafting of phosphate groups.

[0026] Meanwhile, the gradient heating strategy divides the reaction into three stages: a low-temperature stage (40–70℃) preferentially grafts active surface groups; a medium-temperature stage (70–100℃) promotes internal penetration and grafting; and a high-temperature stage (100–150℃) activates deep sites and drives the reaction to equilibrium. The synergy between the ultrasonic field and gradient heating results in significantly better grafting rates (5.70%) and water solubility (76.8%) compared to traditional isothermal modification (grafting rate 3.00%, water solubility 52.4%).

[0027] (3) The three-component synergistic system of “activated humic acid + modified humic acid + ammonium phosphate” achieves activation through multiple pathways. Activated humic acid releases fixed phosphate ions by chelating fixed ions such as calcium, iron, and aluminum. Phosphorylated modified humic acid, due to the introduction of more phosphate groups, has stronger ion competition ability and water solubility, efficiently replacing adsorbed phosphorus and slowing down the fixation of newly applied phosphorus. Ammonium phosphate provides readily available phosphorus, and its phosphate ions form a "common ion atmosphere" with the phosphate groups on modified humic acid, enhancing the phosphorus fixation effect. The three form a "release-protection-replenishment" cycle in the soil, with an activation rate (12.38%) significantly higher than fertilizers containing only activated humic acid (6.52%) or only modified humic acid (7.96%).

[0028] (4) Stable product performance This invention achieves precise control of the activation degree through a standardized activation process. The combined use of activated humic acid and modified humic acid forms a "double insurance" activation mechanism. The batch-to-batch coefficient of variation (7.82%) is significantly lower than that of the control product (15.16%), effectively overcoming the problem of unstable activation effect in existing technologies.

[0029] (5) The preparation process is simple. The physical-chemical synergistic activation uses conventional ball milling equipment, and the ultrasonic-assisted gradient temperature grafting modification uses a reaction vessel equipped with an ultrasonic generator. Subsequent mixing and molding are all conventional processes in fertilizer production. The process flow is continuous and controllable, making it suitable for large-scale industrial production. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1: Physicochemical synergistic activation treatment Take 1000g of weathered coal humic acid raw material (purchased from Wuhai Lvke Biotechnology Co., Ltd., total humic acid ≥50%, organic matter ≥60%), and pulverize it through a 60-mesh sieve. Add 50g of potassium hydroxide (i.e., 5wt%), mix evenly, and then load it into a planetary ball mill. Add zirconium oxide ball milling media to the milling jar, with a ball-to-material ratio of 10:1. Set the milling speed to 80 rpm and the milling time to 90 minutes. After milling, remove the material to obtain activated humic acid.

[0032] Example 2: Physicochemical synergistic activation treatment Take 1000g of weathered coal humic acid raw material (purchased from Wuhai Lvke Biotechnology Co., Ltd., total humic acid ≥50%, organic matter ≥60%), and pulverize it through an 80-mesh sieve. Add 30g of sodium carbonate (3wt%), mix thoroughly, and then load it into a vibrating ball mill. The ball mill jar is filled with steel balls as the grinding media, with a ball-to-material ratio of 8:1. Set the vibration frequency to 25Hz and the milling time to 60 minutes. After milling, remove the material to obtain activated humic acid.

[0033] Example 3: Physicochemical synergistic activation treatment Take 1000g of weathered coal humic acid raw material (purchased from Wuhai Lvke Biotechnology Co., Ltd., total humic acid ≥50%, organic matter ≥60%), and pulverize it through a 40-mesh sieve. Add 80g of ammonia water (concentration 25%) (i.e., 8wt%), mix evenly, and then load it into a stirred ball mill. The ball mill jar is filled with zirconia balls as media, with a ball-to-material ratio of 12:1. Set the stirring speed to 100 rpm and ball mill for 45 minutes under liquid-phase assisted grinding conditions. After ball milling, remove the material and dry it at 60℃ until the moisture content is below 5%, thus obtaining activated humic acid.

[0034] Comparative Example 1: Single Physical Activation Treatment Take 1000g of the same weathered coal humic acid raw material as in Example 1, and crush it through a 60-mesh sieve. Without adding any chemical activator, directly load it into a planetary ball mill and ball mill it under the same conditions (ball-to-material ratio 10:1, rotation speed 80 rpm, time 90 minutes) to obtain physically activated humic acid.

[0035] Comparative Example 2: Single Chemical Activation Treatment Take 1000g of the same weathered coal humic acid raw material as in Example 1, and crush it through a 60-mesh sieve. Add 50g of potassium hydroxide (i.e., 5wt%), mix evenly, and stir and react for 90 minutes in a water bath at 80℃ without ball milling to obtain chemically activated humic acid.

[0036] Activation effect comparison The total acidic group content of the activated humic acids obtained in Examples 1-3 and Comparative Examples 1-2 was determined by acid-base titration, with unactivated humic acids used as a control. The results are shown in Table 1.

[0037] Table 1. Total acidic group content of humic acid under different activation treatments

[0038] As shown in Table 1, the physical-chemical synergistic activation treatment in Examples 1-3 significantly increased the total acidic group content of humic acid (42.2%–69.4%) compared to single physical activation (22.1%) and single chemical activation (31.6%). In particular, Example 1 achieved a total acidic group content of 6.98 meq / g, a 69.4% increase compared to the unactivated form, and increases of 38.8% and 28.8% compared to single physical and single chemical activation, respectively, fully demonstrating the synergistic effect of physical and chemical activation.

[0039] Example 4: Ultrasonic Field Assisted Gradient Temperature Grafting Modification Take 500g of the activated humic acid prepared in Example 1, add 25g of 85% phosphoric acid (i.e., 5% of the mass of the activated humic acid), mix well, and place in a reactor equipped with an ultrasonic generator. Purge the reactor with nitrogen to replace the air inside. Under nitrogen protection, turn on the ultrasonic generator, setting the ultrasonic power to 300W and the ultrasonic frequency to 40kHz. Under ultrasonic field assistance, carry out the grafting reaction according to the following gradient heating program: the first stage is heated to 60℃ and reacted for 1 hour; the second stage is heated to 85℃ and reacted for 2 hours; the third stage is heated to 120℃ and reacted for 1 hour. After the reaction is completed, cool to room temperature to obtain phosphorylated modified humic acid.

[0040] Example 5: Ultrasonic Field Assisted Gradient Temperature Grafting Modification Take 500g of the activated humic acid prepared in Example 2, add 40g of potassium dihydrogen phosphate (i.e., 8%), mix well, and place in a reactor equipped with an ultrasonic generator. Purge the reactor with nitrogen to replace the air inside. Under nitrogen protection, turn on the ultrasonic generator, setting the ultrasonic power to 200W and the ultrasonic frequency to 60kHz. Under ultrasonic field assistance, carry out the grafting reaction according to the following gradient heating program: first stage: heat to 50℃, react for 1.5 hours; second stage: heat to 80℃, react for 2.5 hours; third stage: heat to 110℃, react for 1.5 hours. After the reaction is complete, cool to room temperature to obtain phosphorylated modified humic acid.

[0041] Example 6: Ultrasonic Field Assisted Gradient Temperature Grafting Modification Take 500g of the activated humic acid prepared in Example 3, add 10g of polyphosphoric acid (i.e., 2%), mix well, and place in a reactor equipped with an ultrasonic generator. Purge the reactor with nitrogen to replace the air inside. Under nitrogen protection, turn on the ultrasonic generator, setting the ultrasonic power to 400W and the ultrasonic frequency to 25kHz. Under ultrasonic field assistance, carry out the grafting reaction according to the following gradient heating program: first stage: heat to 65℃, react for 0.5 hours; second stage: heat to 90℃, react for 1.5 hours; third stage: heat to 130℃, react for 0.5 hours. After the reaction is complete, cool to room temperature to obtain phosphorylated modified humic acid.

[0042] Comparative Example 3: Conventional isothermal phosphorylation modification (without ultrasonic assistance) Take 500g of activated humic acid, the same as in Example 4, add 25g of 85% phosphoric acid, mix well and place in a conventional reaction vessel (without an ultrasonic generator). Under nitrogen protection, stir and react at a constant temperature of 120°C for 4 hours (the total reaction time is the same as the total time of gradient heating in Example 4) to obtain phosphorylated modified humic acid.

[0043] Comparative Example 4: Ultrasonic-assisted isothermal phosphorylation modification (without gradient heating) Take 500g of the same activated humic acid as in Example 4, add 25g of 85% phosphoric acid, mix well, and place in a reactor equipped with an ultrasonic generator. Under nitrogen protection, turn on the ultrasonic generator, set the ultrasonic power to 300W, and the ultrasonic frequency to 40kHz. React at a constant temperature of 120℃ for 4 hours to obtain phosphorylated modified humic acid.

[0044] Comparative Example 5: Gradient-temperature phosphorylation modification (without ultrasonic assistance) Take 500g of activated humic acid, the same as in Example 4, add 25g of 85% phosphoric acid, mix well and place in a conventional reaction vessel (without an ultrasonic generator). Under nitrogen protection, react according to the same gradient temperature program as in Example 4 (60℃×1h→85℃×2h→120℃×1h) to obtain phosphorylated modified humic acid.

[0045] Comparison of Modification Effects The phosphorus content (grafting rate index) of the phosphorylated modified humic acids obtained in Examples 4-6 and Comparative Examples 3-5 was determined using the phosphomolybdic blue colorimetric method, and the phosphate grafting rate was calculated based on the increase in phosphorus content. Simultaneously, the water solubility of each sample was determined (expressed as the percentage of solubility in distilled water at 25°C). The results are shown in Table 2.

[0046] Table 2. Grafting rate and water solubility of phosphorylated humic acid under different modification methods

[0047] As can be seen from Table 2: (1) The ultrasonic field-assisted gradient temperature grafting modification in Examples 4-6 significantly improved the grafting rate of phosphate groups. The phosphorus content in Example 4 increased from 0.12% to 5.82%, with an increase of 5.70%, which is 1.90 times that of Comparative Example 3 (conventional isothermal, increase of 3.00%), 1.28 times that of Comparative Example 4 (ultrasound + isothermal, increase of 4.44%), and 1.44 times that of Comparative Example 5 (gradient temperature without ultrasound, increase of 3.96%).

[0048] (2) The water solubility of Example 4 reached 76.8%, which was 46.6% higher than that of Comparative Example 3 (52.4%), 16.7% higher than that of Comparative Example 4 (65.8%), and 27.6% higher than that of Comparative Example 5 (60.2%). The significant increase in water solubility means that the modified humic acid is easier to diffuse and migrate in the soil solution, which is conducive to its full contact with soil particles.

[0049] (3) The grafting rate of Comparative Example 4 (ultrasound + constant temperature) (4.44%) was higher than that of Comparative Example 5 (gradient temperature without ultrasound, 3.96%), indicating that the auxiliary effect of the ultrasonic field was better than that of the simple gradient temperature strategy in improving the grafting rate. However, the grafting rate of Example 4 (ultrasound + gradient temperature) (5.70%) was significantly higher than that of Comparative Example 4 (4.44%) and Comparative Example 5 (3.96%). The difference between the two (1.26% and 1.74%) fully demonstrates that there is a significant synergistic effect between ultrasonic field assistance and gradient temperature grafting. The ultrasonic field promotes the penetration and diffusion of phosphorylation reagent, and the gradient temperature achieves staged and orderly grafting. The combination of the two produces a "1+1>2" effect.

[0050] Example 7: Preparation of Humic Acid-Containing Value-Added Fertilizer Weigh the following components by weight: 20 parts of activated humic acid prepared in Example 1, 10 parts of phosphorylated modified humic acid prepared in Example 4, 65 parts of monoammonium phosphate, 3 parts of zeolite powder, and 2 parts of ammonium citrate.

[0051] Add all the above components to a mixer and mix thoroughly (mixing time 15-20 minutes). Feed the mixture into a rotary drum granulator for granulation, spraying in an appropriate amount of water (approximately 5%-8% of the total material volume) during granulation, and controlling the granulation temperature at 50-60℃. Feed the granulated particles into a dryer and dry them at 80-100℃ until the moisture content is below 3%. Screen the dried particles and collect particles with a diameter of 2.0-4.75mm as the product, which is the humic acid-containing value-added fertilizer.

[0052] Example 8: Preparation of Humic Acid-Containing Value-Added Fertilizer Weigh the following components by weight: 15 parts of activated humic acid prepared in Example 2, 15 parts of phosphorylated modified humic acid prepared in Example 5, 60 parts of diammonium phosphate, 5 parts of zeolite powder, and 5 parts of polyglutamic acid.

[0053] Add all the above components into a mixer and mix thoroughly. Feed the mixture into a disc granulator for granulation, controlling the disc inclination angle at 45–55° and the rotation speed at 15–25 rpm. Dry the granulated particles at 80–100°C until the moisture content is below 3%, and sieve to obtain particles with a diameter of 2.0–4.75 mm as the product.

[0054] Example 9: Preparation of Humic Acid-Containing Value-Added Fertilizer Weigh the following components by weight: 25 parts of activated humic acid prepared in Example 3, 5 parts of phosphorylated modified humic acid prepared in Example 6, 55 parts of monoammonium phosphate, 10 parts of diammonium phosphate, 3 parts of ammonium citrate, and 2 parts of zeolite powder.

[0055] Add all the above components to a mixer and mix thoroughly. Feed the mixture into an extrusion granulator for granulation, with an extrusion pressure of 8–12 MPa. Dry the granulated particles at 80–100°C until the moisture content is below 3%, and sieve to obtain particles with a diameter of 2.0–4.75 mm as the product.

[0056] Comparative Example 6: Fertilizer containing only activated humic acid (excluding modified humic acid) Weigh the following components by weight: 30 parts of activated humic acid prepared in Example 1, 65 parts of monoammonium phosphate, 3 parts of zeolite powder, and 2 parts of ammonium citrate. Prepare the fertilizer according to the same method as in Example 7.

[0057] Comparative Example 7: Fertilizer containing only modified humic acid (excluding activated humic acid) Weigh the following components by weight: 30 parts of phosphorylated modified humic acid prepared in Example 4, 65 parts of monoammonium phosphate, 3 parts of zeolite powder, and 2 parts of ammonium citrate. Prepare the fertilizer according to the same method as in Example 7.

[0058] Comparative Example 8: Fertilizer containing traditional modified humic acid (prepared using the method of Comparative Example 3) Weigh the following components by weight: 20 parts of activated humic acid prepared in Example 1, 10 parts of phosphorylated modified humic acid prepared in Comparative Example 3 (using a conventional constant-temperature, non-ultrasonic method), 65 parts of monoammonium phosphate, 3 parts of zeolite powder, and 2 parts of ammonium citrate. Prepare the fertilizer using the same method as in Example 7.

[0059] Comparative Example 9: Fertilizer containing unactivated humic acid (control) Weigh the following components by weight: 30 parts of unactivated weathered coal humic acid raw material, 65 parts of monoammonium phosphate, 3 parts of zeolite powder, and 2 parts of ammonium citrate. Prepare the fertilizer according to the same method as in Example 7.

[0060] Comparative Example 10: Commercially available ordinary ammonium phosphate fertilizer Commercially available monoammonium phosphate (64% total nutrients) was selected as a control.

[0061] Performance testing 1. Soil insoluble phosphorus activation rate test

[0062] Test Method: Typical calcareous soil (pH 8.2, available phosphorus content 5.6 mg / kg, total phosphorus content 620 mg / kg) was collected, air-dried, and passed through a 2 mm sieve. 200 g of soil sample was weighed and added to fertilizer samples prepared in Examples 7-9 and Comparative Examples 6-10, respectively, with a fertilizer application rate calculated at 100 mg / kg P₂O₅ per kg soil. After thorough mixing, the sample was incubated in a 25°C incubator. Samples were taken on days 7, 14, and 28 of incubation, and the available phosphorus content of the soil was determined using the Olsen method.

[0063] The activation rate of sparingly soluble phosphorus is calculated using the following formula: Activation rate (%) = (available phosphorus content in fertilized soil - available phosphorus content in unfertilized control soil) / total phosphorus content in soil × 100% The results are shown in Table 3.

[0064] Table 3. Activation rate (%) of insoluble phosphorus in soil by different fertilizer samples

[0065] As can be seen from Table 3: (1) The humic acid-containing value-added fertilizers in Examples 7-9 showed significantly higher activation rates of insoluble phosphorus in the soil than the comparative examples. After 28 days of cultivation, the activation rate of Example 7 reached 12.38%, which was 1.90 times that of Comparative Example 6 (activated humic acid only, 6.52%), 1.56 times that of Comparative Example 7 (modified humic acid only, 7.96%), 1.41 times that of Comparative Example 8 (traditional modified humic acid, 8.75%), 3.48 times that of Comparative Example 9 (unactivated humic acid, 3.56%), and 8.54 times that of Comparative Example 10 (ordinary ammonium phosphate, 1.45%).

[0066] (2) The activation rate of Example 7 (12.38%) was significantly higher than the simple average of the sum of Comparative Example 6 (6.52%) and Comparative Example 7 (7.96%) (7.24%), and much higher than that of the single component, indicating that the combination of activated humic acid and modified humic acid produced a significant synergistic effect.

[0067] (3) The activation rate of Example 7 (humic acid modified by ultrasonic-assisted gradient heating) (12.38%) was significantly higher than that of Comparative Example 8 (humic acid modified by conventional constant temperature without ultrasonic modification, 8.75%), which was 41.5% higher. This result fully demonstrates the significant effect of the ultrasonic field-assisted gradient heating grafting modification technology of the present invention on improving the phosphorus activation performance of humic acid.

[0068] (4) In terms of cultivation time, the activation rate of each embodiment continued to increase with the extension of time (maintaining an increasing trend from 7 days to 28 days), indicating that the fertilizer of the present invention has a continuous activation ability; while the activation rate of Comparative Example 10 (ordinary ammonium phosphate) decreased slightly after 14 days of cultivation, indicating that phosphorus was refixed after ordinary ammonium phosphate was applied to the soil, further proving the protective and activation effect of the fertilizer of the present invention on phosphorus.

[0069] 2. Product performance stability test To verify the performance stability of the product of this invention under different humic acid raw material sources, three batches of products were prepared using humic acid raw materials from three different sources: weathered coal humic acid (purchased from Wuhai Lvke Biotechnology Co., Ltd., total humic acid ≥50%, organic matter ≥60%), lignite humic acid (purchased from Zhaotong Kaili Humic Acid Co., Ltd., total humic acid ≥50%, organic matter ≥60%), and peat humic acid (purchased from Guiyang Wudang District Yiyuan Mining Co., Ltd., total humic acid ≥50%, organic matter ≥60%), according to the formulation and process of Example 7. Simultaneously, three batches of control products were prepared according to the formulation and process of Comparative Example 6 (containing only activated humic acid, without modified humic acid). The activation rate of each batch of product for insoluble phosphorus in soil was measured (after 28 days of incubation), and the inter-batch coefficient of variation was calculated. The results are shown in Table 4.

[0070] Table 4. Batch stability of product activation rate under different raw material sources

[0071] As shown in Table 4, the batch-to-batch coefficient of variation of the product of this invention is 7.82%, significantly lower than the 15.16% of the control product. This indicates that through the organic combination of physical-chemical synergistic activation and ultrasonic-assisted gradient temperature grafting modification, as well as the synergistic cooperation between activated humic acid and modified humic acid, the product of this invention can maintain stable activation performance under different raw material sources, effectively overcoming the problem of unstable humic acid activation effect in the prior art.

[0072] Pot experiment To verify the effect of the fertilizer of this invention on promoting phosphorus absorption and growth in crops, a pot experiment was conducted on corn.

[0073] Experimental Design: Calcareous soil (pH 8.2, available phosphorus 5.6 mg / kg) was used, and pots were filled (5 kg soil per pot). The following treatments were set: (1) No fertilizer (CK); (2) Ordinary ammonium phosphate (MAP); (3) Fertilizer of Example 7; (4) Fertilizer of Example 8; (5) Fertilizer of Example 9; (6) Fertilizer of Comparative Example 6; (7) Fertilizer of Comparative Example 7; (8) Fertilizer of Comparative Example 8. Each treatment was replicated 3 times. The phosphorus application rate for each fertilization treatment was 150 mg / kg soil P2O5, and nitrogen and potassium fertilizers were supplemented according to the conventional dosage. Corn (variety: Zhengdan 958) was sown, with 3 seedlings per pot. After 60 days of growth, the aboveground biomass and total phosphorus content of the plants were measured. The results are shown in Table 5.

[0074] Table 5. Effects of different fertilization treatments on maize growth and phosphorus uptake.

[0075] As shown in Table 5, the treatments using fertilizers from Examples 7, 8, and 9 resulted in significantly higher aboveground biomass, total phosphorus content, and phosphorus uptake in maize compared to other treatments. Compared to ordinary ammonium phosphate, Example 7 increased aboveground biomass by 71.1% and phosphorus uptake by 157.5%; compared to Comparative Example 6 (activated humic acid only), biomass increased by 36.5% and phosphorus uptake by 75.0%; compared to Comparative Example 7 (modified humic acid only), biomass increased by 26.2% and phosphorus uptake by 52.2%; and compared to Comparative Example 8 (traditional modified humic acid), biomass increased by 20.9% and phosphorus uptake by 39.1%. Pot experiments further confirmed that the fertilizers of this invention, by activating insoluble phosphorus in the soil and increasing phosphorus availability, can significantly promote phosphorus absorption and crop growth.

[0076] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0077] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A humic acid-containing value-added fertilizer for activating insoluble phosphorus in soil, characterized in that, By weight, it contains the following components: 5-30 parts activated humic acid, 3-20 parts phosphoric acid modified humic acid, 50-90 parts ammonium phosphate, and 1-10 parts activation aid.

2. The humic acid-containing value-added fertilizer according to claim 1, characterized in that, The activated humic acid is prepared by physical-chemical synergistic activation treatment of humic acid raw materials. The specific activation process is as follows: after pulverizing the humic acid raw materials, a chemical activator is added, and ball milling activation is carried out in a ball mill.

3. The humic acid-containing value-added fertilizer according to claim 2, characterized in that, The chemical activator is selected from one or more of potassium hydroxide, sodium carbonate, and ammonia water, and the amount of chemical activator added is 0.5% to 10% of the mass of humic acid raw material.

4. The humic acid-containing value-added fertilizer according to claim 1, characterized in that, The phosphorylated modified humic acid is prepared by grafting the activated humic acid of claim 2 with a phosphorylation reagent under ultrasonic field assistance through a gradient temperature increase; the phosphorylation reagent is selected from one or more of phosphoric acid, phosphate, and polyphosphoric acid; the ultrasonic field assistance has an ultrasonic power of 100-500W and an ultrasonic frequency of 20-80kHz.

5. The humic acid-containing value-added fertilizer according to claim 4, characterized in that, The gradient temperature grafting modification reaction includes the following steps: activating humic acid and phosphorylation reagent are mixed at a mass ratio of 100:1 to 100:20, and the grafting reaction is carried out under ultrasonic field assistance according to a gradient temperature program: the first stage is carried out at 40 to 70°C for 0.5 to 2 hours, the second stage is carried out at 70 to 100°C for 1 to 3 hours, and the third stage is carried out at 100 to 150°C for 0.5 to 2 hours to obtain phosphorylated modified humic acid.

6. The humic acid-containing value-added fertilizer according to claim 1, characterized in that, The ammonium phosphate is selected from one or two of monoammonium phosphate and diammonium phosphate; the activating agent is selected from one or more of zeolite powder, ammonium citrate, and polyglutamic acid.

7. A method for preparing a humic acid-containing value-added fertilizer as described in any one of claims 1-6, characterized in that, Includes the following steps: (1) Physical-chemical synergistic activation treatment of humic acid raw materials to obtain activated humic acid; (2) The activated humic acid obtained in step (1) is subjected to gradient temperature grafting modification with phosphorylation reagent under the assistance of ultrasonic field to obtain phosphorylated modified humic acid. (3) Mix the activated humic acid obtained in step (1), the phosphorylated modified humic acid obtained in step (2), ammonium phosphate and the activation aid in a certain proportion; (4) The mixture obtained in step (3) is processed into the humic acid-containing value-added fertilizer.

8. The preparation method according to claim 7, characterized in that, The physical-chemical synergistic activation treatment in step (1) includes: crushing the humic acid raw material through a 40-100 mesh sieve, adding a chemical activator, and ball milling and activating it in a ball mill; The chemical activator is selected from one or more of potassium hydroxide, sodium carbonate, and ammonia water, and the amount of chemical activator added is 0.5% to 10% of the mass of humic acid raw material.

9. The preparation method according to claim 7, characterized in that, The ultrasonic field-assisted gradient temperature grafting modification described in step (2) is carried out under a protective atmosphere, which is selected from nitrogen and argon. The specific modification process is as follows: the activated humic acid and the phosphorylation reagent are mixed at a mass ratio of 100:1 to 100:

20. Under the assistance of an ultrasonic field with an ultrasonic power of 100 to 500 W and an ultrasonic frequency of 20 to 80 kHz, the grafting reaction is carried out according to the gradient temperature program: the first stage is 40 to 70 °C for 0.5 to 2 h, the second stage is 70 to 100 °C for 1 to 3 h, and the third stage is 100 to 150 °C for 0.5 to 2 h. The phosphorylation reagent is selected from one or more of phosphoric acid, phosphate, and polyphosphoric acid.

10. The application of the humic acid-containing value-added fertilizer according to any one of claims 1-6 or the humic acid-containing value-added fertilizer prepared by the method according to any one of claims 7-9, characterized in that, The application is in any of the following directions: (1) Activate insoluble phosphorus in the soil; (2) Increase the available phosphorus content in the soil; (3) Promotes the absorption of phosphorus by crops and / or promotes crop growth.

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