Attapulgite composite slow-release urea acid soil remediation agent and preparation method thereof

Abstract

This invention relates to the field of soil remediation technology, and particularly to an attapulgite composite slow-release urea acidic soil remediation agent and its preparation method. The remediation agent, by weight, comprises 25-35 parts urea, 80-120 parts attapulgite clay, 4-6 parts quaternary ammonium berberine, 2-5 parts L-selenomethionine, 15-26 parts soluble starch, 13-24 parts polyvinyl alcohol, 8-13 parts glycerol, and 4-6 parts 37% citric acid solution. The attapulgite is modified by intercalation with quaternary ammonium berberine, and then L-selenomethionine is loaded through mechanochemical loading to obtain a dense composite coating material with an active functional surface. By coating it onto the surface of urea particles, quaternary ammonium berberine forms a dense hydrophobic slow-release layer through hydrophobic modification and cation exchange, effectively extending the nitrogen dissolution cycle. At the same time, L-selenomethionine fills the micropores of the membrane layer, enhancing the membrane barrier performance, so that the remediation agent has multiple functions, including long-term slow-release nitrogen supply, acid soil improvement, and biological selenium supplementation.

Description

Technical Field

[0001] This invention relates to the field of soil remediation technology, and in particular to an attapulgite composite slow-release urea acidic soil remediation agent and its preparation method. Background Technology

[0002] Soil acidification is one of the major forms of soil degradation restricting agricultural production globally. Acidic soils are widely distributed in southern my country, covering approximately one-fifth of the country's land area. Acidic soils exhibit significantly elevated concentrations of active aluminum and exchangeable hydrogen ions, severely inhibiting crop root development and nutrient absorption. Simultaneously, they lead to the fixation of available phosphorus, substantial leaching of basic ions, and increased heavy metal activity, resulting in a continuous decline in soil fertility and reduced yield and quality of agricultural products. Traditional methods for improving acidic soils primarily focus on applying lime-based substances to rapidly raise soil pH by neutralizing soil acidity and precipitating active aluminum, while also supplementing calcium and magnesium to some extent. In addition, there have been attempts to improve acidic soils by applying organic conditioners such as biochar and organic fertilizers.

[0003] However, lime-based soil conditioners have significant shortcomings in practical applications: their action period is short, alkaline release is concentrated, and long-term excessive application can easily lead to soil compaction, nutrient availability imbalance, and damage to the microbial community. While organic conditioners such as biochar can increase soil organic matter content and improve soil structure, their own nutrient content is low, and their acid-regulating ability is limited when applied alone, making it difficult to achieve both rapid remediation and long-term fertilization of acidified soils. Therefore, there is an urgent need to develop a remediation agent with multiple functions, including acid regulation, slow nutrient release, and soil structure improvement, to achieve continuous and efficient remediation of acidic soils. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an attapulgite composite slow-release urea acidic soil remediation agent and its preparation method, thereby solving the technical problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] An attapulgite composite slow-release urea acidic soil remediation agent is made from the following components in parts by weight:

[0007] 25-35 parts urea, 80-120 parts attapulgite clay, 4-6 parts quaternary ammonium berberine, 2-5 parts L-selenomethionine, 15-26 parts soluble starch, 13-24 parts polyvinyl alcohol, 8-13 parts glycerol, and 4-6 parts citric acid solution with a mass fraction of 37%.

[0008] The weight ratio of the attapulgite clay to the quaternary ammonium berberine is 20:1.

[0009] In one possible implementation, it is made from the following components in parts by weight: 30 parts urea, 100 parts attapulgite clay, 5 parts quaternary ammonium berberine, 5 parts L-selenomethionine, 20 parts soluble starch, 18 parts polyvinyl alcohol, 10 parts glycerol, and 5 parts citric acid solution with a mass fraction of 37%.

[0010] In one possible implementation, the molecular weight of the polyvinyl alcohol is 120,000 to 150,000.

[0011] In one possible implementation, the repair agent consists of particles comprising, from the inside out, a urea core, a modified attapulgite inner coating layer, and a composite binder outer coating layer.

[0012] In one possible implementation, a method for preparing an attapulgite composite slow-release urea acidic soil remediation agent includes the following steps:

[0013] S1. Weigh soluble starch, polyvinyl alcohol, and glycerol according to the ratio, add them to distilled water, heat to 90℃ and stir until completely dissolved, add 37% citric acid solution and continue stirring until uniform, then add distilled water to dilute and obtain composite adhesive BGJ-1 for later use.

[0014] S2. Add attapulgite clay to water and perform ultrasonic dissociation and dispersion to obtain attapulgite suspension. Add quaternary ammonium berberine to the suspension, continue ultrasonic treatment, and then perform vacuum low-temperature drying. After drying, grind and sieve to obtain quaternary ammonium berberine modified attapulgite ATP-1.

[0015] S3. The quaternary ammonium berberine-modified attapulgite ATP-1 obtained in step S2 is mixed with L-selenomethionine and placed in a stirred mill. It is first mixed at low speed and then ground at high speed to load L-selenomethionine onto the surface and pores of the modified attapulgite. After grinding, it is sieved to obtain L-selenomethionine-loaded modified attapulgite ATP-2.

[0016] S4. The modified attapulgite ATP-2 loaded with L-selenomethionine obtained in step S3 is added together with large granulated urea into a round pot granulator. Water is sprayed onto the surface of the material by atomization, so that the modified attapulgite is coated on the surface of urea layer by layer. The machine continues to operate until a dense and uniform coating layer is formed. The coated urea intermediate ATP-2-U is discharged.

[0017] S5. Place the coated urea intermediate obtained in step S4 into a fluidized bed, and spray the composite binder prepared in step S1 into it using a top spray method for secondary coating. After the spraying is completed, vacuum dry it, cool it and unload it to obtain the attapulgite composite slow-release urea acid soil remediation agent B-ATP-2-U.

[0018] In one possible implementation, in step S1, soluble starch, polyvinyl alcohol, and glycerol are added to 380 parts of distilled water and kept warm at a stirring rate of 400 rpm until completely dissolved. Then, a 37% citric acid solution is added and stirring is continued for 15 minutes. Finally, 500 parts of distilled water are added for dilution.

[0019] In one possible implementation, in step S2, the conditions for ultrasonic dissociation and dispersion are a frequency of 40 kHz, a power of 300 W, and a duration of 30 minutes; after adding quaternary ammonium berberine, the treatment continues for another 30 minutes under the same ultrasonic conditions; the conditions for depressurized low-temperature drying are a temperature of -50°C and a pressure of less than 10 Pa; and the material is then ground and passed through a 200-mesh sieve.

[0020] In one possible implementation, in step S3, the stirring mill speed is first set to 200 rpm and run for 10 minutes to complete the initial mixing, and then the speed is increased to 10,000 rpm for strong grinding for 10 minutes; after grinding, it is passed through a 2000-mesh vibrating screen.

[0021] In one possible implementation, in step S4, the particle size range of the large urea particles is 2.00mm-4.75mm; the operating parameters of the round pot granulator are a rotation speed of 30 rpm and an inclination angle of 45°; the weight of the water sprayed in is 15 parts, and the machine continues to run for 10 minutes after the spraying is completed.

[0022] In one possible implementation, in step S5, the inlet air temperature of the fluidized bed is set to 60°C; the injection rate of the composite binder is 4 mL / min; and the vacuum drying conditions are -0.08 MPa pressure, 60°C temperature, and 40 minutes drying time.

[0023] Beneficial effects compared to existing technologies:

[0024] 1. In this scheme, attapulgite is modified by intercalation with quaternary ammonium berberine, and then subjected to mechanochemical loading of L-selenomethionine to form a composite coating material with a dense structure and an active functional surface. After this coating material is applied to the surface of urea particles, the quaternary ammonium berberine, through hydrophobic modification and cation exchange, constructs a dense hydrophobic slow-release layer around the urea, significantly extending the dissolution period of nitrogen nutrients. At the same time, the introduction of L-selenomethionine further fills the micropores of the membrane layer, improving the overall barrier performance of the coating layer, enabling the repair agent to have both ultra-long-lasting slow-release and selenium supplementation functions.

[0025] 2. In this scheme, a composite binder is prepared using soluble starch, polyvinyl alcohol, and glycerol as raw materials. A secondary coating process, involving pan granulation and fluidized bed coating, is used to form a continuous, structurally complete, and layered coating layer on the urea surface using modified attapulgite. This coating layer gradually reacts with hydrogen ions and active aluminum ions in acidic soils, releasing calcium and magnesium ions to neutralize soil acidity. Simultaneously, the layered chain structure of attapulgite adsorbs and immobilizes active aluminum, effectively reducing aluminum toxicity and achieving slow-release, long-lasting acidification of acidic soils.

[0026] 3. In this solution, the attapulgite composite slow-release urea acidic soil remediation agent organically integrates nitrogen slow release, acidity conditioning, and selenium nutrient supplementation. After application to acidic soil, it increases soil pH, reduces active aluminum content, and continuously supplies crops with the nitrogen and selenium nutrients they require for growth. This remediation agent effectively improves the rhizosphere microecological environment of crops, promotes root development and nutrient absorption, significantly increases crop yield and quality, and possesses excellent economic benefits and promising prospects for widespread application. Attached Figure Description

[0027] 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.

[0028] Figure 1 This is a schematic diagram of the preparation process of B-ATP-2-U according to the present invention;

[0029] Figure 2 This is a scanning electron microscope schematic diagram of the surface of the B-ATP-2-U particles of the present invention;

[0030] Figure 3 This is a schematic diagram showing the comparison of the growth of the control group and the experimental group of Chinese cabbage plants after 35 days of cultivation using B-ATP-2-U in acidic soil. Detailed Implementation

[0031] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be noted that these embodiments are only used to explain the present invention and are not intended to limit the scope of the present invention. In the following description, unless otherwise specified, "parts" refers to parts by weight. The acidic soils used were all dried at 100°C to a moisture content of less than 1% before the experiment to eliminate the interference of initial moisture differences on the experimental results. For the sake of brevity, attapulgite clay will be abbreviated as ATP below.

[0032] This invention provides an attapulgite composite slow-release urea acidic soil remediation agent, which is made from the following components in parts by weight: 25-35 parts urea, 80-120 parts attapulgite clay ATP, 4-6 parts quaternary ammonium berberine, 2-5 parts L-selenomethionine, 15-26 parts soluble starch, 13-24 parts polyvinyl alcohol, 8-13 parts glycerol, and 4-6 parts citric acid solution with a mass fraction of 37%; and the weight ratio of attapulgite clay to quaternary ammonium berberine is 20:1.

[0033] Example 1:

[0034] This embodiment is the optimal embodiment, and the product exhibits the best overall performance. An attapulgite composite slow-release urea acidic soil remediation agent is made from the following components in parts by weight: 30 parts urea, 100 parts attapulgite clay, 5 parts quaternary ammonium berberine, 5 parts L-selenomethionine, 20 parts soluble starch, 18 parts polyvinyl alcohol, 10 parts glycerol, and 5 parts a 37% citric acid solution.

[0035] The specific preparation method of the repair agent in this embodiment is as follows:

[0036] Step S1: Preparation of composite adhesive BGJ-1

[0037] Weigh out 20 parts of soluble starch, 18 parts of polyvinyl alcohol with a molecular weight between 120,000 and 150,000, and 10 parts of glycerol according to the above proportions, and add them together to 380 parts of distilled water. Heat the mixture to 90°C and maintain the temperature at a stirring rate of 400 rpm until all components are completely dissolved, resulting in a transparent and homogeneous solution. Then, add 5 parts of a 37% citric acid solution to this solution and continue stirring for 15 minutes to ensure homogeneity. Finally, add 500 parts of distilled water for dilution and mix thoroughly to obtain the composite adhesive, designated BGJ-1, for later use.

[0038] Step S2: Preparation of quaternary ammonium berberine-modified ATP-1

[0039] 100 parts of ATP were added to 200 parts of tap water and dispersed using an ultrasonic cell disruptor at a frequency of 40 kHz and a power of 300 W for 30 minutes to obtain an ATP suspension. Subsequently, 5 parts of quaternary ammonium berberine were added to this suspension, and the mixture was treated under the same ultrasonic conditions for another 30 minutes to ensure sufficient interaction between the quaternary ammonium berberine and ATP. The resulting mixture was then subjected to reduced pressure drying at -50°C and below 10 Pa until all moisture was removed. The dried solid block was ground and passed through a 200-mesh sieve to obtain quaternary ammonium berberine-modified ATP, denoted as ATP-1.

[0040] Step S3: Preparation of modified ATP-2 loaded with L-selenomethionine

[0041] Weigh 100 parts of the ATP-1 powder obtained in step S2 and place it together with 5 parts of L-selenomethionine into a stirred mill. First, set the stirring mill speed to 200 rpm and run it for 10 minutes to complete the initial mixing of the two materials; then increase the speed to 10,000 rpm and grind vigorously at this high speed for 10 minutes, using mechanochemical action to firmly load L-selenomethionine onto the surface and pores of ATP-1. After grinding, collect all the powder and sieve it using a 2000-mesh vibrating sieve to ensure that all of it passes through. The resulting product is designated as ATP-2.

[0042] Step S4: Preparation of the coated urea intermediate ATP-2-U

[0043] Weigh 70 parts of the ATP-2 powder obtained in step S3 and 30 parts of commercially available large-particle urea with a particle size range of 2.00mm-4.75mm, and add them together to a round pot granulator. The operating parameters of the round pot granulator are set as follows: rotation speed 30 rpm, inclination angle 45°. After starting the equipment, evenly spray 15 parts of water onto the continuously tumbling material surface through an atomizing nozzle, allowing the ATP-2 powder to gradually coat the surface of the large-particle urea under the action of water. After spraying, continue running for 10 minutes until a dense and uniform coating layer forms on the particle surface. After discharge, the coated urea intermediate is obtained, denoted as ATP-2-U.

[0044] Step S5: Preparation of attapulgite composite slow-release urea acidic soil remediation agent B-ATP-2-U

[0045] Weigh 500 parts of ATP-2-U obtained in step S4 and place them in a fluidized bed. Set the inlet air temperature to 60℃ to ensure the ATP-2-U particles are in a stable fluidized state under the action of the airflow. Using a top spray method, spray 100 parts of the binder BGJ-1 prepared in step S1 into the fluidized bed at a constant rate of 4 mL / min to perform a secondary coating on the ATP-2-U particles. After spraying, start the vacuum system and continue drying for 40 minutes at a pressure of -0.08 MPa and a temperature of 60℃. After cooling, unload the material to obtain the attapulgite composite slow-release urea acidic soil remediation agent, denoted as B-ATP-2-U.

[0046] Example 2:

[0047] An attapulgite composite slow-release urea acidic soil remediation agent is made from the following components in parts by weight: 25 parts urea, 120 parts attapulgite clay ATP, 6 parts quaternary ammonium berberine, 2 parts L-selenomethionine, 15 parts soluble starch, 13 parts polyvinyl alcohol, 8 parts glycerol, and 4 parts citric acid solution with a mass fraction of 37%.

[0048] The preparation method of the repair agent in this embodiment is the same as that in Example 1.

[0049] Example 3:

[0050] An attapulgite composite slow-release urea acidic soil remediation agent is made from the following components in parts by weight: 35 parts urea, 80 parts attapulgite clay, 4 parts quaternary ammonium berberine, 5 parts L-selenomethionine, 26 parts soluble starch, 24 parts polyvinyl alcohol, 13 parts glycerol, and 6 parts citric acid solution with a mass fraction of 37%.

[0051] The preparation method of the repair agent in this embodiment is the same as that in Example 1.

[0052] The remediation agents prepared in Examples 1, 2, and 3 were used in a comparative experiment on acidic soil remediation under the same application conditions. The soil pH and 100% urea leaching time were tested after 30 days. The results showed that the soil pH of the product from Example 1 increased to 7.01, with a leaching time of 140 days; the soil pH of the product from Example 2 increased to 6.62, with a leaching time of 112 days; and the soil pH of the product from Example 3 increased to 6.87, with a leaching time of 126 days. It is evident that Example 1 showed the best overall balance in adjusting acidity to near neutrality and the nitrogen slow-release cycle, with the longest leaching time and pH closest to 7.0. Therefore, the following characterization and performance tests will all be conducted using the product from Example 1.

[0053] Product Characterization and Judgment

[0054] The final product B-ATP-2-U was taken and its surface morphology was observed using a scanning electron microscope. The photographs are shown below. Figure 2 As shown. Figure 2 This study demonstrates a typical microstructure of a coating layer composed of interwoven and stacked nanorod-shaped ATP particles. This coating layer uniformly and completely covers the particle surface, exhibiting a porous and rough morphology with no exposed areas of urea crystals. This morphological feature indicates that the modified attapulgite has successfully coated the urea core surface, forming a dense and continuous coating structure.

[0055] Further analysis of the application performance tests in Table 1 below shows that after application to acidic soil, the B-ATP-2-U product not only significantly increased the soil pH from 5.35 to 7.01, but also achieved 100% urea leaching within 140 days, far exceeding the comparative studies. Based on the combined SEM microstructure and macroscopic slow-release acid-regulating performance, it can be determined that the modification effects of each step in this embodiment have been achieved, and the final product B-ATP-2-U was successfully prepared.

[0056] Application performance testing and comparative analysis

[0057] To verify the effectiveness of the technical solution of this invention and determine the irreplaceability of each step, multiple comparative examples were constructed under the same testing conditions and their performance was compared with that of the product in Example 1. The preparation steps of each comparative example are described below:

[0058] Comparative Example 1

[0059] A repair agent, whose preparation steps are basically the same as those in Example 1, the only difference being that in step S2, 5 parts of quaternary ammonium berberine are replaced with an equal part of sodium hydroxide (NaOH), while the other raw materials, ratios and operating parameters remain unchanged.

[0060] Comparative Example 2

[0061] A repair agent is prepared in a manner similar to that of Example 1, except that L-selenomethionine is not added in step S3. Specifically, 100 parts of ATP-1 obtained in step S2 are directly ground separately, with the grinding speed and time consistent with S3 of this example. After grinding, the powder is passed through a 2000-mesh sieve and replaces ATP-2 in subsequent steps S4 and S5.

[0062] Comparative Example 3

[0063] A repair agent was prepared using essentially the same steps as in Example 1, except that the pan granulation and encapsulation process in step S4 was omitted. Instead, 70 parts of the ATP-2 powder obtained in step S3 and 30 parts of commercially available large-particle urea were directly added to a V-type mixer and mixed at 200 rpm for 15 minutes at room temperature to obtain a physical mixture. Then, following the same procedure as in this example, the mixture was placed in a fluidized bed, sprayed with 100 parts of BGJ-1, and vacuum dried.

[0064] Comparative Example 4

[0065] A repair agent, whose preparation steps are basically the same as those in Example 1, the only difference being that in step S4, the 70 parts of ATP-2 used are replaced with an equal amount of ATP raw ore powder that has only been dry mechanically pulverized and passed through a 2000-mesh sieve, while the other steps and conditions remain unchanged.

[0066] Comparative Example 5

[0067] A soil conditioner is prepared by directly weighing 500 parts of commercially available large-particle urea into a fluidized bed, and spraying only 100 parts of the composite binder BGJ-1 obtained in step S1 onto its surface at a spraying rate of 4 mL / min. The mixture is then vacuum dried to obtain the final product. No ATP material of any kind is used in this comparative example.

[0068] The soil remediation performance and nitrogen slow-release performance of the products from Example 1 and each comparative example were uniformly tested. The original acidic soil used had an initial pH of 5.4 after pretreatment. The test methods are as follows:

[0069] Accurately weigh 100 portions of dry acidic soil and add 1 portion of B-ATP-2-U from Example 1, the product of Comparative Example 1, the product of Comparative Example 2, the product of Comparative Example 3, the product of Comparative Example 4, and the product of Comparative Example 5 to each portion. Mix thoroughly and set up a blank control without any remedy. Adjust the soil moisture content of all treatment groups to 35% with deionized water, stir evenly, and place in a constant temperature incubator at 25℃ for 30 days of static aging. On the 30th day, take samples, extract at a soil-to-water ratio of 1:2.5, and measure the pH value, recording the endpoint pH value. At the same time, the time required for 100% urea to be leached out in each treatment group was tested using the soil column leaching method. The specific operation is as follows: weigh 100 portions of aged soil from each treatment group and put them into an organic glass leaching column with an inner diameter of 5cm and a height of 30cm. The bottom of the column is pre-laid with a 2cm high layer of quartz sand and a layer of nylon filter screen. Starting from day 1, 20 mL of deionized water was injected daily from the top of the column at a constant rate of 10 mL / h using a micro-peristaltic pump, and all eluent was collected at the bottom of the column. The cumulative amount of urea in the eluent was determined using the p-dimethylaminobenzaldehyde spectrophotometric method. The number of days required to reach 100% of the theoretical urea addition amount for each remedial agent was recorded. The test results are summarized in Table 1.

[0070] Table 1. Soil pH and 100% urea leaching time after 30 days for each treatment group

[0071]

[0072] As shown in Table 1, the original soil pH was 5.35 after 30 days of cultivation, which was still relatively acidic. After applying the product of Example 1 of this invention, the soil pH significantly increased to 7.01, successfully adjusting to the neutral range, and its urea leaching time was as long as 140 days, demonstrating both excellent acid-regulating effect and ultra-long nitrogen slow-release capability.

[0073] Compared with Comparative Example 1, Example 1, which only replaced quaternary ammonium berberine with sodium hydroxide, achieved a final soil pH of 6.91 and reduced urea leaching time to 124 days. This indicates that quaternary ammonium berberine not only provides alkalinity, but its unique quaternary ammonium cation and aromatic ring structure can optimize the interlayer microenvironment of ATP through hydrophobic modification and cation exchange, forming a denser and hydrophobic slow-release barrier layer, thus making a decisive contribution to extending the controlled-release period.

[0074] Compared with Comparative Example 2, Example 1 omitted the loading of L-selenomethionine, resulting in a sharp drop in soil pH to 6.53 and a leaching time of only 70 days. This strongly demonstrates that during the high-energy grinding process in step S3, L-selenomethionine can chemically bond and physically adsorb onto the active sites on the ATP surface through its amino and carboxyl groups, effectively filling the micropores of the coating layer and improving the membrane density. This step not only endows the remediation agent with selenium supplementation function but also significantly enhances the physical barrier properties of the coating layer structurally.

[0075] Compared with Comparative Example 3, Example 1 used a simple mixing process instead of the round pot granulation coating, resulting in a reduction of the leaching time from 140 days to 113 days. This indicates that the round pot granulation process in step S4 utilizes rolling and atomization wetting to coat the ATP-2 powder layer by layer uniformly onto the urea core surface, forming a continuous membrane shell with integrity and gradient structure. Simple physical mixing cannot achieve this structure, resulting in a significant reduction in the sustained-release effect.

[0076] Compared with Comparative Example 4, Example 1 directly used unmodified ATP raw mineral powder, with a sustained-release time of only 43 days and very limited acid-adjusting ability. This reflects that natural ATP obtained by simply pulverizing it is far from meeting the requirements as a highly efficient sustained-release repair agent due to insufficient active sites and poor film-forming properties, thus highlighting the necessity of activation and functional modification in steps S2 and S3.

[0077] Compared with Comparative Example 5, Example 5, which only used a soluble organic binder to coat urea, had the shortest sustained-release time of only 12 days. This indicates that BGJ-1, composed of starch, polyvinyl alcohol, etc., is extremely prone to swelling and dissolving in water, making it impossible to construct a long-lasting water-blocking layer. The core functional component in this invention that achieves continuous acid adjustment and ultra-long sustained release is precisely the ATP composite coating layer with a dense layered structure, which has undergone organic functionalization modification.

[0078] Examples of potted plant applications

[0079] To further demonstrate the improvement effect of the remediation agent of this invention on acidic soil, a pot experiment was conducted on Chinese cabbage. The test soil was the same as described above, with an initial pH of 5.4. Two treatments were set up in the experiment: the control group used 1000 g of dry acidic soil directly; the experimental group was prepared by thoroughly mixing 10 g (i.e., 1% of the total soil weight) of product B-ATP-2-U from Example 1 with 1000 g of acidic soil and then potting it.

[0080] The pots used for potted plants have a top diameter of 11cm, a bottom diameter of 9.4cm, and a height of 12.9cm. Five pre-germinated seeds of four-season butter bok choy are sown per pot, with a final spacing of 3 seedlings per pot after germination. All potted plants are cultivated in an artificial climate chamber with the following conditions: daytime temperature 26℃, nighttime temperature 20℃, 14 hours of light per day, light intensity 30,000 lux, and relative humidity 70%. Deionized water is added daily using a weighing method to maintain soil moisture content at 60% to 65% of field capacity.

[0081] Observations were conducted after 35 days of cultivation, and the plants were compared in the following photos: Figure 3 As shown. Figure 3 In the image, the left side shows representative plants from the acidic soil control group, exhibiting typical symptoms of stunted growth, weak physique, yellowing leaves, and inhibited growth. The right side shows plants from the experimental group treated with the product of this invention, showing significantly increased plant height and crown width, more abundant and dark green leaves, and vigorous growth. This direct comparison fully demonstrates that after applying the remediation agent of this invention, soil acidity is effectively eliminated, root nutrient supply and microecological environment are fundamentally improved, thereby comprehensively promoting the vegetative growth of Chinese cabbage.

[0082] Finally, it should be noted that the above embodiments are merely examples for clearly illustrating the present invention and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An attapulgite composite slow-release urea acidic soil remediation agent, characterized in that, It is made from the following components in parts by weight: 25-35 parts urea, 80-120 parts attapulgite clay, 4-6 parts quaternary ammonium berberine, 2-5 parts L-selenomethionine, 15-26 parts soluble starch, 13-24 parts polyvinyl alcohol, 8-13 parts glycerol, and 4-6 parts citric acid solution with a mass fraction of 37%. The weight ratio of the attapulgite clay to the quaternary ammonium berberine is 20:

1.

2. The attapulgite composite slow-release urea acidic soil remediation agent as described in claim 1, characterized in that, It is made from the following components in parts by weight: 30 parts urea, 100 parts attapulgite clay, 5 parts quaternary ammonium berberine, 5 parts L-selenomethionine, 20 parts soluble starch, 18 parts polyvinyl alcohol, 10 parts glycerol, and 5 parts citric acid solution with a mass fraction of 37%.

3. The attapulgite composite slow-release urea acidic soil remediation agent as described in claim 1, characterized in that, The molecular weight of the polyvinyl alcohol is 120,000 to 150,000.

4. The attapulgite composite slow-release urea acidic soil remediation agent as described in claim 1, characterized in that, The repair agent consists of particles comprising, from the inside out, a urea core, a modified attapulgite inner coating layer, and a composite adhesive outer coating layer.

5. A method for preparing an attapulgite composite slow-release urea acidic soil remediation agent as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Weigh soluble starch, polyvinyl alcohol, and glycerol according to the ratio, add them to distilled water, heat to 90℃ and stir until completely dissolved, add 37% citric acid solution and continue stirring until uniform, then add distilled water to dilute and obtain composite adhesive BGJ-1 for later use. S2. Add attapulgite clay to water and perform ultrasonic dissociation and dispersion to obtain attapulgite suspension. Add quaternary ammonium berberine to the suspension, continue ultrasonic treatment, and then perform vacuum low-temperature drying. After drying, grind and sieve to obtain quaternary ammonium berberine modified attapulgite ATP-1. S3. The quaternary ammonium berberine-modified attapulgite ATP-1 obtained in step S2 is mixed with L-selenomethionine and placed in a stirred mill. It is first mixed at low speed and then ground at high speed to load L-selenomethionine onto the surface and pores of the modified attapulgite. After grinding, it is sieved to obtain L-selenomethionine-loaded modified attapulgite ATP-2. S4. The modified attapulgite ATP-2 loaded with L-selenomethionine obtained in step S3 is added together with large granulated urea into a round pot granulator. Water is sprayed onto the surface of the material by atomization, so that the modified attapulgite is coated on the surface of urea layer by layer. The machine continues to operate until a dense and uniform coating layer is formed. The coated urea intermediate ATP-2-U is discharged. S5. Place the coated urea intermediate obtained in step S4 into a fluidized bed, and spray the composite binder prepared in step S1 into it using a top spray method for secondary coating. After the spraying is completed, vacuum dry it, cool it and unload it to obtain the attapulgite composite slow-release urea acid soil remediation agent B-ATP-2-U.

6. The preparation method of the attapulgite composite slow-release urea acidic soil remediation agent as described in claim 5, characterized in that, In step S1, soluble starch, polyvinyl alcohol, and glycerol are added to 380 parts of distilled water and kept warm at a stirring rate of 400 rpm until completely dissolved. After adding a 37% citric acid solution, stirring is continued for 15 minutes, and then 500 parts of distilled water are added for dilution.

7. The preparation method of the attapulgite composite slow-release urea acidic soil remediation agent as described in claim 5, characterized in that, In step S2, the conditions for ultrasonic dissociation and dispersion are a frequency of 40kHz, a power of 300W, and a duration of 30 minutes; after adding quaternary ammonium berberine, the treatment continues for another 30 minutes under the same ultrasonic conditions; the conditions for vacuum low-temperature drying are a temperature of -50℃ and a pressure of less than 10Pa; and the material is then ground and passed through a 200-mesh sieve.

8. The preparation method of the attapulgite composite slow-release urea acidic soil remediation agent as described in claim 5, characterized in that, In step S3, the stirring mill is first set to 200 rpm and run for 10 minutes to complete the initial mixing. Then the speed is increased to 10,000 rpm for strong grinding for 10 minutes. After grinding, the mixture is passed through a 2000-mesh vibrating screen.

9. The preparation method of the attapulgite composite slow-release urea acidic soil remediation agent as described in claim 5, characterized in that, In step S4, the particle size range of the large urea particles is 2.00mm-4.75mm; the operating parameters of the round pot granulator are a rotation speed of 30 rpm and an inclination angle of 45°; the weight of the water sprayed in is 15 parts, and the machine continues to run for 10 minutes after the spraying is completed.

10. The preparation method of the attapulgite composite slow-release urea acidic soil remediation agent as described in claim 5, characterized in that, In step S5, the inlet air temperature of the fluidized bed is set to 60°C; the injection rate of the composite binder is 4 mL / min; and the vacuum drying conditions are -0.08 MPa pressure, 60°C temperature, and 40 minutes drying time.

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