Environment-friendly urea slow-release fertilizer and preparation method thereof

Abstract

The application belongs to the technical field of fertilizers, and particularly relates to an environment-friendly urea slow-release fertilizer and a preparation method thereof. The preparation method of the urea slow-release fertilizer comprises the following steps: S1. Modified sodium-based montmorillonite is added to water, and a modified sodium-based montmorillonite suspension is obtained after ultrasonic dispersion; urea and puhuizi polysaccharide are uniformly mixed and preheated to obtain mixed particles; S2. The modified sodium-based montmorillonite suspension is sprayed on the surface of the mixed particles, and the environment-friendly urea slow-release fertilizer is obtained after drying. The method is simple and easy to operate, and the obtained fertilizer has excellent slow-release performance.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer technology, specifically relating to an environmentally friendly slow-release urea fertilizer and its preparation method. Background Technology

[0002] Urea, as the most widely used solid nitrogen fertilizer with the highest nitrogen content globally, plays a crucial role in modern agricultural production and is one of the core materials for ensuring food security and high and stable crop yields. However, the inherent defects exposed after the application of traditional urea have become a prominent contradiction restricting sustainable agricultural development and ecological environmental protection. The core problem lies in the severe mismatch between the excessively rapid release rate and the stage-specific nutrient needs of crops. After urea is applied to the soil, it is usually rapidly hydrolyzed into ammonium nitrogen within a few days under the action of urease, leading to a sharp increase in local nitrogen concentration in the soil in a short period of time. Crop seedlings have limited absorption capacity, and a large amount of unutilized nitrogen is lost mainly through three pathways: ammonia volatilization, nitrification-denitrification (producing greenhouse gas N2O), and nitrate leaching. Studies have shown that the average nitrogen utilization rate of traditional urea in the current season is only 30-35%, which not only results in a staggering waste of valuable fertilizer resources (millions of tons annually) and increases agricultural production costs, but also triggers a series of serious environmental problems: eutrophication of water bodies, soil acidification, air pollution, and increased greenhouse gas emissions.

[0003] To address this contradiction, the research and development of "slow-release" and "controlled-release" fertilizers has emerged and become a cutting-edge and important direction in the fertilizer industry and agricultural technology fields for nearly half a century. Slow-release fertilizers aim to regulate the kinetics of nutrient release through physical, chemical, or biochemical means, synchronizing the release pattern as closely as possible with the crop's absorption curve. Existing technological approaches can be mainly categorized as follows: first, physical coating, such as using sulfur, polymer resins, or natural cementing materials to encapsulate urea particles, controlling nutrient diffusion through membrane thickness and permeability; second, chemical synthesis, such as preparing urea-formaldehyde condensates (UF, IBDU, etc.), relying on their slow chemical decomposition in the soil to release nitrogen; and third, carrier adsorption / immobilization, such as loading urea onto porous materials like zeolite, attapulgite, and biochar. Although these technologies have improved nitrogen utilization efficiency to varying degrees (some reaching 60%-70%), they still face significant challenges. For example, many polymer-coated materials suffer from high costs, poor degradation in soil, and even microplastic pollution; some chemically synthesized slow-release fertilizers release too slowly initially, failing to meet the early nutrient requirements of crops; while some mineral carrier materials have drawbacks such as low nutrient loading rates and unstable release cycles. Therefore, developing a novel slow-release urea that is efficient, environmentally friendly, cost-effective, and whose release curve closely matches crop needs is a crucial technological bottleneck that urgently needs to be overcome for the green development of agriculture.

[0004] In view of this, the present invention provides an environmentally friendly urea slow-release fertilizer and its preparation method, which realizes the precise and long-term release of fertilizer nutrients, promotes crop growth, and contributes to the green and efficient development of agriculture. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the first objective of this invention is to provide an environmentally friendly method for preparing urea slow-release fertilizer, which has a simple process.

[0006] The second objective of this invention is to provide an environmentally friendly urea slow-release fertilizer with excellent slow-release performance.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing an environmentally friendly urea slow-release fertilizer includes the following steps: S1. Modified sodium montmorillonite was added to water and ultrasonically dispersed to obtain a modified sodium montmorillonite suspension; urea and fan palm polysaccharide were mixed evenly and preheated to obtain mixed particles; S2. The modified sodium-based montmorillonite suspension is sprayed onto the surface of the mixed particles and dried to obtain the environmentally friendly urea slow-release fertilizer.

[0008] Preferably, the preparation method of the modified sodium-based montmorillonite in step S1 is as follows: A. Add sodium montmorillonite to water, adjust the pH and stir, heat to 70-80℃ and then add hexadecyltrimethylammonium bromide to react, to obtain a pretreated sodium montmorillonite suspension; B. Add corn starch to water, stir to obtain a starch suspension, adjust the pH and then add methyl epoxy stearate and heat to react, to obtain a modified starch solution; C. Add the pretreated sodium-based montmorillonite suspension to the modified starch solution, shake and dry to obtain the modified sodium-based montmorillonite.

[0009] This invention utilizes the ring-opening etherification reaction between the epoxy group of methyl epoxy stearate and the hydroxyl group of starch molecules to introduce a long hydrophobic chain with an ester group into the starch skeleton, thereby obtaining a hydrophobic modified starch solution. Subsequently, it is reacted with sodium montmorillonite pretreated with CTAB to obtain modified sodium montmorillonite.

[0010] Preferably, the mass ratio of hexadecyltrimethylammonium bromide to sodium montmorillonite in step A is 1:(5-8).

[0011] Preferably, in step A, the pH is adjusted to 9-11; the stirring time is 1-2 hours; and the reaction time is 2-3 hours.

[0012] Preferably, the corn starch in the starch suspension in step B has a mass fraction of 8-10 wt%; and the amount of methyl epoxy stearate added is 10-12 wt% of the mass of corn starch.

[0013] Preferably, in step B, the pH is adjusted to 8-9; the heating reaction temperature is 70-85℃, and the time is 4-6 hours.

[0014] Preferably, the mass ratio of the pretreated sodium-based montmorillonite suspension to the modified starch solution in step C is 1:(1.5-2).

[0015] Preferably, in step S1, the mass ratio of urea, fan palm polysaccharide, and modified sodium montmorillonite is (50-60):(5-10):(8-17); and the mass ratio of modified sodium montmorillonite and water is 1:(10-15).

[0016] Preferably, the ultrasonic dispersion time in step S1 is 0.5-1 h; the preheating temperature is 50-60 °C and the time is 10-20 min.

[0017] An environmentally friendly urea slow-release fertilizer was prepared using the above-mentioned preparation method.

[0018] Compared with the prior art, the main advantages of the present invention are as follows: 1. This invention provides a method for preparing environmentally friendly slow-release urea fertilizer using urea, fan palm seed polysaccharide, and modified sodium montmorillonite as raw materials. This preparation method is simple and easy to implement. Furthermore, sodium montmorillonite and fan palm seed polysaccharide are both natural biological macromolecules, green and renewable, and can be completely biodegraded without leaving any pollution residues, thus avoiding the damage to soil ecology caused by chemical additives.

[0019] 2. This invention combines fan palm seed polysaccharide with modified sodium montmorillonite to enhance the slow-release performance of fertilizers. Specifically, this invention uses modified sodium montmorillonite as a coating layer, which, after CTAB cationic intercalation and hydrophobic modification with methyl epoxy stearate, forms an organic-inorganic interpenetrating network structure. This significantly prolongs the release pathway of urea molecules, hindering rapid water molecule penetration and free diffusion of urea molecules. Simultaneously, the enhanced hydrophobicity effectively blocks soil moisture from contacting urea, thus achieving a slow-release effect. As a natural biomacromolecule, fan palm seed polysaccharide's polar groups such as hydroxyl and carboxyl groups on its molecular chain can form hydrogen bonds with urea molecules, delaying urea dissolution.

[0020] 3. This invention combines fan palm seed polysaccharide with modified sodium montmorillonite to enhance crop yield. Specifically, fan palm seed polysaccharide, as a natural biomolecule, provides a carbon source for soil microorganisms, promoting the reproduction of beneficial soil bacteria. Simultaneously, the polysaccharide molecules can chelate fixed phosphorus, potassium, and other elements in the soil, converting them into readily absorbable nutrients for crops, thus effectively promoting crop growth. The slow-release effect of the coating layer ensures that nutrient supply meets the crop's growth needs while reducing nitrogen loss, achieving a stable and long-lasting nutrient supply, thereby significantly promoting crop growth. Attached Figure Description

[0021] Figure 1 Here is a SEM image of the modified sodium-based montmorillonite prepared in Example 1; Figure 2 These are the experimental results of slow-release fertilizers prepared in water, as shown in the examples and comparative examples. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to specific embodiments. However, those skilled in the art should understand that the following embodiments are only for illustrating the present invention and should not be regarded as limiting the present invention. Specific conditions not specified in the embodiments are performed according to conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the reagents or instruments used are all conventional products obtained through commercial channels.

[0023] The urea of ​​this invention has a particle size of 4-5 mm; The preparation method of Fan palm seed polysaccharide is as follows: Crush the seeds of *Livistona chinensis* and extract twice with 10 times the volume of 95% ethanol under reflux for 2 hours each time. Dry the residue after extraction, add 20 times the volume of deionized water, and enzymatically hydrolyze in a water bath at 50°C for 30 minutes, followed by inactivation at 80°C for 10 minutes. Filter to obtain the extract. Sonicate the extract for 30 minutes, then concentrate it to 20% of its original volume. Add 4 times the volume of anhydrous ethanol and let it stand overnight at 4°C. Wash the filter residue sequentially with anhydrous ethanol, ether, and acetone, and dry to obtain *Livistona chinensis* polysaccharide.

[0024] Example 1 A modified sodium-based montmorillonite, prepared by the following method: A. Sodium montmorillonite was ultrasonically dispersed in deionized water at a mass ratio of CTAB to sodium montmorillonite of 1:7 to achieve a nano-montmorillonite concentration of 5wt%. Then, a 12wt% sodium carbonate solution was added dropwise to adjust the pH to 10. The mixture was magnetically stirred for 1.5 hours, heated to 75°C, and then slowly added cetyltrimethylammonium bromide (CTAB). After reacting for 2.5 hours, a pretreated sodium montmorillonite suspension was obtained. B. Add the dried corn starch to deionized water and stir magnetically to obtain a starch suspension with a corn starch mass fraction of 9 wt%. Then, add a 12 wt% sodium carbonate solution to adjust the pH to 8.5. Add methyl epoxy stearate to the mixture slowly at an amount of 11 wt% of the corn starch mass, heat to 80℃ and react for 5 hours to obtain a modified starch solution. C. The pretreated sodium-based montmorillonite suspension was added to the modified starch solution at a mass ratio of 1:1.7. After ultrasonic vibration and drying, the modified sodium-based montmorillonite was obtained. The SEM image of the modified sodium-based montmorillonite is shown below. Figure 1 As shown.

[0025] Example 2 A modified sodium-based montmorillonite, prepared by the following method: A. Using CTAB and sodium montmorillonite in a mass ratio of 1:5, sodium montmorillonite was ultrasonically dispersed in deionized water to achieve a nano-montmorillonite concentration of 4wt%. Then, a 10wt% sodium carbonate solution was added dropwise to adjust the pH to 9. The mixture was magnetically stirred for 1 hour, and after heating to 70℃, CTAB was slowly added. After reacting for 3 hours, a pretreated sodium montmorillonite suspension was obtained. B. Add the dried corn starch to deionized water and stir magnetically to obtain a starch suspension with a corn starch mass fraction of 8 wt%. Then, add a 10 wt% sodium carbonate solution to adjust the pH to 8. Add methyl epoxy stearate to the mixture slowly at a concentration of 10 wt% of the corn starch mass, heat to 70℃ and react for 6 hours to obtain a modified starch solution. C. The pretreated sodium montmorillonite suspension is added to the modified starch solution at a mass ratio of 1:1.5. After ultrasonic vibration and drying, the modified sodium montmorillonite is obtained.

[0026] Example 3 A modified sodium-based montmorillonite, prepared by the following method: A. Using CTAB and sodium montmorillonite in a mass ratio of 1:8, sodium montmorillonite was ultrasonically dispersed in deionized water to achieve a nano-montmorillonite concentration of 6wt%. Then, a 15wt% sodium carbonate solution was added dropwise to adjust the pH to 11. The mixture was magnetically stirred for 2 hours, and after heating to 80℃, CTAB was slowly added. After reacting for 2 hours, a pretreated sodium montmorillonite suspension was obtained. B. Add the dried corn starch to deionized water and stir magnetically to obtain a starch suspension with a corn starch mass fraction of 10 wt%. Then, add a 15 wt% sodium carbonate solution to adjust the pH to 9. Add methyl epoxy stearate to the mixture slowly at an amount of 12 wt% of the corn starch mass, heat to 85℃ and react for 4 hours to obtain a modified starch solution. C. The pretreated sodium montmorillonite suspension is added to the modified starch solution at a mass ratio of 1:2. After ultrasonic vibration and drying, the modified sodium montmorillonite is obtained.

[0027] Example 4 A method for preparing an environmentally friendly urea slow-release fertilizer includes the following steps: S1. Weigh the raw materials according to the mass ratio of urea, fan palm polysaccharide and modified sodium montmorillonite 54:7:12 and set aside; add modified sodium montmorillonite to deionized water at a mass ratio of 1:12, and ultrasonically disperse for 0.8 h to obtain a modified sodium montmorillonite suspension; mix urea and fan palm polysaccharide evenly, preheat at 55℃ for 15 min to obtain mixed particles; S2. The modified sodium-based montmorillonite suspension is uniformly sprayed onto the surface of the mixed particles, and dried to obtain the environmentally friendly urea slow-release fertilizer.

[0028] An environmentally friendly urea slow-release fertilizer was prepared using the above-mentioned preparation method.

[0029] Example 5 A method for preparing an environmentally friendly urea slow-release fertilizer includes the following steps: S1. Weigh the raw materials according to the mass ratio of urea, fan palm polysaccharide and modified sodium montmorillonite 50:5:8 and set aside; add modified sodium montmorillonite to deionized water at a mass ratio of 1:10, and ultrasonically disperse for 0.5 h to obtain a modified sodium montmorillonite suspension; mix urea and fan palm polysaccharide evenly, preheat at 50℃ for 20 min to obtain mixed particles; S2. The modified sodium-based montmorillonite suspension is uniformly sprayed onto the surface of the mixed particles, and dried to obtain the environmentally friendly urea slow-release fertilizer.

[0030] An environmentally friendly urea slow-release fertilizer was prepared using the above-mentioned preparation method.

[0031] Example 6 A method for preparing an environmentally friendly urea slow-release fertilizer includes the following steps: S1. Weigh the raw materials according to the mass ratio of urea, fan palm polysaccharide and modified sodium montmorillonite 60:10:17 and set aside; add modified sodium montmorillonite to deionized water at a mass ratio of 1:15, and ultrasonically disperse for 1 hour to obtain a modified sodium montmorillonite suspension; mix urea and fan palm polysaccharide evenly, preheat at 60℃ for 10 minutes to obtain mixed particles; S2. The modified sodium-based montmorillonite suspension is uniformly sprayed onto the surface of the mixed particles, and dried to obtain the environmentally friendly urea slow-release fertilizer.

[0032] An environmentally friendly urea slow-release fertilizer was prepared using the above-mentioned preparation method.

[0033] Comparative Example 1 The difference between Comparative Example 1 and Example 4 is that the fan palm polysaccharide is omitted in step S1.

[0034] Comparative Example 2 The difference between Comparative Example 2 and Example 4 is that in step S1, a physical mixture of sodium montmorillonite and corn starch is used instead of the modified sodium montmorillonite in Example 1, and the ratio of the two is the same as in Example 1.

[0035] Experimental Example 1 A slow-release experiment was conducted in water on the fertilizers prepared in the examples and comparative examples. The specific experimental procedure is as follows: Accurately weigh 1g of the fertilizer prepared in the examples or comparative examples and place it into a dialysis bag (cutoff value 100). Place each dialysis bag into an Erlenmeyer flask and add 200mL of deionized water. Incubate in a constant temperature shaker. At regular intervals, take 2mL of the test solution from the Erlenmeyer flask and simultaneously add 2mL of deionized water. Detect the urea content in each test solution using the p-dimethylaminobenzaldehyde colorimetric method to calculate the urea release amount in each sample. Plot the relationship curve between release time (t) and urea release amount (see Table 1). Figure 2 .

[0036] Table 1 Figure 2 The figures show the results of the slow-release experiments in water using fertilizers prepared in the examples and comparative examples. See Table 1 for observations. Figure 2It can be seen that, compared with Comparative Examples 1-2, the fertilizer prepared in Example 1 has a superior slow-release effect. The above results indicate that *Livistona chinensis* polysaccharide and modified sodium montmorillonite can improve the slow-release performance of fertilizers. This is because the coating layer of the fertilizer of this invention is modified sodium montmorillonite, which, after CTAB cationic intercalation and hydrophobic modification with methyl epoxide, forms an organic-inorganic interpenetrating network structure, greatly extending the release path of urea molecules and hindering the rapid penetration of water molecules and the free diffusion of urea molecules. At the same time, the enhanced hydrophobicity effectively blocks soil moisture from contacting urea, thereby achieving a slow-release effect. *Livistona chinensis* polysaccharide, as a natural biological macromolecule, has polar groups such as hydroxyl and carboxyl groups on its molecular chain that can form hydrogen bonds with urea molecules, delaying urea dissolution. The combined use of these two ingredients can significantly improve the slow-release performance of the fertilizer.

[0037] Experiment Example 2 The effects of the fertilizers prepared in the examples and comparative examples were tested, and the specific experimental procedures are as follows: 2.1 Experimental Procedure The maize variety used was Nongda 108. Field trials were conducted on brown soil, and its physicochemical properties are shown in Table 2. Each experimental plot was 5m × 5m in size and randomly arranged. Planting began in late April. Fertilizers prepared according to the examples and comparative proportions were applied at a rate of 12 kg / mu during the seedling, tasseling, and grain-filling stages. A control group without fertilizer was also included. After the maize matured, 30 plants were randomly selected from each plot for yield measurement. The results are shown in Table 3.

[0038] Table 2 Table 3 As shown in Table 3, compared with Comparative Examples 1-2, the application of the slow-release fertilizer in Example 1 significantly increased corn yield. These results demonstrate that the combined use of fan palm seed polysaccharide and modified sodium montmorillonite can improve crop yield. Specifically, fan palm seed polysaccharide, as a natural biomolecule, can provide a carbon source for soil microorganisms and promote the reproduction of beneficial soil bacteria. Simultaneously, polysaccharide molecules can chelate fixed phosphorus, potassium, and other elements in the soil, converting them into available nutrients that crops can absorb, thereby effectively promoting crop growth. The slow-release effect of the coating layer ensures that nutrient supply meets the crop's growth needs and reduces nitrogen loss, achieving a stable and long-lasting nutrient supply, thus significantly promoting crop growth.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. The basic principles and main features of the present invention have been described above with specific implementation schemes. Based on the present invention, some modifications or substitutions can be made, but these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of protection claimed by the present invention.

Claims

1. A method for preparing an environmentally friendly urea slow-release fertilizer, characterized in that, Includes the following steps: S1. Modified sodium montmorillonite was added to water and ultrasonically dispersed to obtain a modified sodium montmorillonite suspension; urea and fan palm polysaccharide were mixed evenly and preheated to obtain mixed particles; S2. The modified sodium-based montmorillonite suspension is sprayed onto the surface of the mixed particles and dried to obtain the environmentally friendly urea slow-release fertilizer.

2. The preparation method of the environmentally friendly urea slow-release fertilizer as described in claim 1, characterized in that, The preparation method of the modified sodium-based montmorillonite in step S1 is as follows: A. Add sodium montmorillonite to water, adjust the pH and stir, heat to 70-80℃ and then add hexadecyltrimethylammonium bromide to react, to obtain a pretreated sodium montmorillonite suspension; B. Add corn starch to water, stir to obtain a starch suspension, adjust the pH and then add methyl epoxy stearate and heat to react, to obtain a modified starch solution; C. Add the pretreated sodium-based montmorillonite suspension to the modified starch solution, shake and dry to obtain the modified sodium-based montmorillonite.

3. The preparation method of the environmentally friendly urea slow-release fertilizer as described in claim 2, characterized in that, The mass ratio of hexadecyltrimethylammonium bromide to sodium montmorillonite in step A is 1:(5-8).

4. The preparation method of the environmentally friendly urea slow-release fertilizer as described in claim 2, characterized in that, In step A, the pH is adjusted to 9-11; the stirring time is 1-2 hours; and the reaction time is 2-3 hours.

5. The preparation method of the environmentally friendly urea slow-release fertilizer as described in claim 2, characterized in that, In step B, the corn starch in the starch suspension has a mass fraction of 8-10 wt%; the amount of methyl epoxy stearate added is 10-12 wt% of the corn starch mass.

6. The preparation method of the environmentally friendly urea slow-release fertilizer as described in claim 2, characterized in that, In step B, the pH is adjusted to 8-9; the heating reaction is carried out at a temperature of 70-85°C for 4-6 hours.

7. The preparation method of the environmentally friendly urea slow-release fertilizer as described in claim 2, characterized in that, In step C, the mass ratio of the pretreated sodium-based montmorillonite suspension to the modified starch solution is 1:(1.5-2).

8. The method for preparing the environmentally friendly urea slow-release fertilizer as described in claim 1, characterized in that, In step S1, the mass ratio of urea, fan palm polysaccharide, and modified sodium montmorillonite is (50-60):(5-10):(8-17); and the mass ratio of modified sodium montmorillonite and water is 1:(10-15).

9. The method for preparing the environmentally friendly urea slow-release fertilizer as described in claim 1, characterized in that, The ultrasonic dispersion time in step S1 is 0.5-1h; the preheating temperature is 50-60℃ and the time is 10-20min.

10. An environmentally friendly urea slow-release fertilizer, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

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