Slow-release water-soluble fertilizer and preparation method thereof

Abstract

This invention discloses a slow-release water-soluble fertilizer and its preparation method, belonging to the field of water-soluble fertilizer technology. The slow-release water-soluble fertilizer includes: a mesoporous carrier, a surface functionalization modifier, macronutrient raw materials, micronutrient raw materials, a water-soluble dispersing agent, and a pH adjuster. The preparation method includes: preparing a mesoporous carrier, functionalizing the surface of the mesoporous carrier, and loading the nutrient raw materials into the mesoporous carrier to prepare the finished water-soluble fertilizer. This invention uses a modified mesoporous carrier and constructs an ion-gated slow-release system by grafting pH-responsive functional groups onto its surface. The fertilizer is completely water-soluble and leaves no residue. After entering the soil, the nutrient release rate is triggered according to the change in rhizosphere pH, solving the dual technical problems of rapid nutrient loss in conventional water-soluble fertilizers and poor water solubility in coated slow-release fertilizers, thus improving fertilizer utilization.

Description

Technical Field

[0001] This invention relates to the field of water-soluble fertilizer technology, specifically to a slow-release water-soluble fertilizer and its preparation method. Background Technology

[0002] In current agricultural production, conventional water-soluble fertilizers have the advantages of good water solubility, fast absorption, and compatibility with fertigation. They can dissolve elements such as nitrogen, phosphorus, and potassium and release them into the soil quickly, where they are absorbed by the roots in a short period of time. However, they also have problems such as excessively fast nutrient release, easy leaching with water, low fertilizer utilization, and the need for frequent topdressing. These problems not only increase planting costs but also easily cause soil compaction.

[0003] Currently available slow-release fertilizers mostly employ traditional processes such as resin coating, sulfur coating, and physical encapsulation. These coated slow-release fertilizers suffer from drawbacks such as poor water solubility, easy clogging of drip irrigation nozzles, difficult degradation of coating materials, and mismatch between nutrient release and crop needs, failing to meet the core requirement of rapid dissolution in water-soluble fertilizers. Some chelated water-soluble fertilizers can only stabilize micronutrients, offering no controlled slow-release effect for macronutrients such as nitrogen, phosphorus, and potassium. Furthermore, existing slow-release fertilizers only provide a slow release effect and cannot achieve precise fertilization based on soil environmental properties. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a slow-release water-soluble fertilizer and its preparation method, so as to solve the dual technical problems of rapid nutrient loss of conventional water-soluble fertilizers and poor water solubility of coated slow-release fertilizers, and further improve fertilizer utilization.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows.

[0006] A slow-release water-soluble fertilizer comprises the following raw materials in parts by weight: 35-50 parts of mesoporous carrier; 6-11 parts of surface functionalizing modifier; 38-50 parts of macronutrient raw materials; 4-7 parts of trace element nutrient raw materials; 0.5-1 part of water-soluble dispersant; pH adjuster 0.3-0.5 parts.

[0007] Preferably, the mesoporous carrier comprises the following raw materials in parts by weight: 25-35 parts of attapulgite mesoporous powder, 10-15 parts of zeolite powder, and deionized water, with a material-to-liquid ratio of 1:8.

[0008] Preferably, the surface functionalizing modifier comprises the following raw materials in parts by weight: 3-5 parts of trisodium citrate, 2-4 parts of aminotrimethylphosphonic acid, 1-2 parts of modified sodium alginate, and 3-5 parts of coupling agent.

[0009] Preferably, the macronutrient raw materials include the following parts by weight: 18-23 parts urea, 12-15 parts potassium dihydrogen phosphate, and 8-12 parts potassium nitrate; the micronutrient raw materials include the following parts by weight: 2-3 parts EDTA chelated calcium, 1-2 parts EDTA chelated magnesium, 0.5-0.8 parts chelated iron, 0.3-0.6 parts chelated zinc, and 0.2-0.6 parts chelated boron.

[0010] A method for preparing a slow-release water-soluble fertilizer, specifically including the following steps: S1. Prepare mesoporous supports with a specific surface area ≥220m² / g and a pore size of 2-50nm; S2. Functional modification of the surface of the mesoporous carrier; S3. Load nutrient raw materials into a mesoporous carrier to prepare a water-soluble fertilizer product.

[0011] Preferably, step S1 specifically includes: S11. Mix attapulgite mesoporous powder and zeolite powder in a certain proportion, place them in a high-temperature activation furnace, and calcine at 350-400℃ for 2-3 hours to remove internal impurities and moisture from the minerals, broaden the pore structure, and increase the specific surface area. S12. After calcination, the mineral is cooled to room temperature, deionized water is added at a ratio of 1:8, and the mixture is stirred for 30 minutes. After filtration, the mineral is dried and pulverized into an ultrafine powder of 2000 mesh or finer to obtain the activated mesoporous carrier.

[0012] Preferably, step S2 specifically includes: S21. Preparation of modified sodium alginate; sodium alginate is oxidized with sodium periodate to break the vicinal diol structure on its G unit, generating aldehyde-modified sodium alginate; S22. Activation of trisodium citrate; activation of the carboxyl group of trisodium citrate in an aqueous phase using a coupling agent; S23. Surface functionalization modification of mesoporous carriers.

[0013] Preferably, step S23 specifically includes: S231. Place the mesoporous support prepared in step S1 into a reaction vessel, add an aqueous ethanol solution with a volume ratio of ethanol to water of 7:3; heat to 55-60℃ and stir at a constant temperature; S232. Add aminotrimethylphosphonic acid, modified sodium alginate and activated trisodium citrate in proportion, keep the reaction at the temperature for 1.5-2h, and uniformly graft pH-responsive functional groups onto the surface and inner wall of the mesoporous carrier through chemical bonding to form ion-gated sites. S233. After the reaction is complete, the ethanol solvent is removed by vacuum distillation, the mixture is dried at a low temperature of 60-70℃, and then pulverized through a 2500-mesh sieve to obtain a surface-functionalized modified mesoporous support.

[0014] Preferably, step S3 specifically includes: S31. Mix macronutrient raw materials and micronutrient raw materials in proportion, add deionized water, heat to 45-50℃, stir until completely dissolved, and prepare a nutrient mixed aqueous solution; S32. Slowly add the modified mesoporous support to the nutrient mixed aqueous solution and stir at a constant temperature for 40-50 minutes. Utilize the adsorption and ionic bonding of the mesoporous support to fully load nutrient ions into the pores and gating sites of the support. S33. Add water-soluble dispersant, continue stirring for 15 minutes, and adjust the pH of the mixed solution to 6.0-7.0 with pH adjuster; S34. The mixed solution is fed into a spray drying tower, the inlet air temperature is controlled at 160-180℃ and the outlet air temperature is controlled at 70-80℃, and the ultrafine powder product is obtained by spray drying. S35. After cooling, pass through a 3000-mesh sieve. After passing the inspection, seal and package to obtain slow-release water-soluble fertilizer.

[0015] The technological advancements achieved by this invention are as follows, thanks to the adoption of the above technical solutions.

[0016] This invention uses modified mesoporous minerals as a carrier, which are activated and modified to increase the specific surface area and porosity. Weakly acidic or weakly alkaline pH-responsive functional groups are grafted onto the carrier surface, anchoring nitrogen, phosphorus, potassium, and trace element ions through a combination of chemical bonding and physical adsorption. After the fertilizer dissolves in water, it forms a uniform and transparent aqueous solution without solid residue. When applied to the soil, the pH in the rhizosphere changes dynamically due to root respiration and microbial activity, triggering conformational changes in the functional groups on the carrier surface. Ion-gated channels open, and nutrient ions are gradually released and continuously absorbed by the crop roots. Unreleased nutrients are stably anchored inside the mesoporous carrier, preventing leaching with water, thus achieving long-term slow release and precise supply. This invention solves the dual technical problems of rapid nutrient loss in conventional water-soluble fertilizers and poor water solubility in coated slow-release fertilizers, improving fertilizer utilization. Detailed Implementation

[0017] A slow-release water-soluble fertilizer relies on a surface-functionalized mesoporous carrier to precisely regulate nutrient release through changes in soil pH, rather than passively releasing nutrients at a uniform rate. The release rhythm is highly matched with the nutrient requirements of crops. The mesoporous carrier is a porous material with a pore size between 2 and 50 nanometers. It has a large specific surface area and a controllable pore structure, enabling the simultaneous slow release of large amounts of nitrogen, phosphorus, potassium, and micronutrients. This solves the problem of conventional water-soluble fertilizers where only micronutrients are stable while macronutrients are rapidly lost.

[0018] In this invention, the slow-release water-soluble fertilizer comprises the following raw materials in parts by weight: 35-50 parts of mesoporous carrier; 6-11 parts of surface functionalization modifier; 38-50 parts of macronutrient raw materials; 4-7 parts of micronutrient raw materials; 0.5-1 part of water-soluble dispersant; and 0.3-0.5 parts of pH adjuster.

[0019] The mesoporous carrier comprises the following raw materials in parts by weight: 25-35 parts attapulgite mesoporous powder, 10-15 parts zeolite powder, and deionized water, with a material-to-liquid ratio of 1:8; the surface functionalizing modifier comprises the following raw materials in parts by weight: 3-5 parts trisodium citrate, 2-4 parts aminotrimethylphosphonic acid, 1-2 parts modified sodium alginate, and 3-5 parts coupling agent; the macronutrient raw materials comprise the following raw materials in parts by weight: 18-23 parts urea, 12-15 parts potassium dihydrogen phosphate, and 8-12 parts potassium nitrate; the micronutrient raw materials comprise the following raw materials in parts by weight: 2-3 parts EDTA chelated calcium, 1-2 parts EDTA chelated magnesium, 0.5-0.8 parts chelated iron, 0.3-0.6 parts chelated zinc, and 0.2-0.6 parts chelated boron; the water-soluble dispersing agent is polyaspartic acid, and the pH adjuster is food-grade phosphoric acid.

[0020] In this invention, the mesoporous carrier is prepared using natural mineral raw materials, making the resulting mesoporous carrier biodegradable, free from secondary pollution and heavy metal residues, and does not damage the soil aggregate structure. It is adaptable to various pH soil environments, reduces fertilization frequency, and minimizes agricultural non-point source pollution. The addition of water-soluble dispersing agents enhances the fertilizer's water solubility and dispersibility, accelerates fertilizer dissolution, and eliminates precipitation residues. The addition of pH adjusters makes the fertilizer suitable for the root growth environment of most crops.

[0021] This invention also provides a method for preparing a slow-release water-soluble fertilizer, which specifically includes the following steps: S1. Preparation of mesoporous carriers.

[0022] This step specifically includes: S11. Mix attapulgite mesoporous powder and zeolite powder in a certain proportion, put them into a high-temperature activation furnace, and calcine them at 350-400℃ for 2-3 hours to remove impurities and moisture inside the minerals, broaden the pore structure, increase the specific surface area to ≥220m² / g, and the pore size to 2-50nm, which is suitable for the construction of ion adsorption and gated channels.

[0023] S12. After calcination, the mineral is cooled to room temperature, deionized water is added at a ratio of 1:8, and the mixture is stirred for 30 minutes. After filtration, the mineral is dried and pulverized into an ultrafine powder of 2000 mesh or finer to obtain the activated mesoporous carrier.

[0024] S2. Functionalize the surface of the mesoporous carrier.

[0025] This step specifically includes: S21. Preparation of modified sodium alginate: Sodium alginate is oxidized with sodium periodate to break the vicinal diol structure on its G unit, generating aldehyde-modified sodium alginate.

[0026] S22. Activation of trisodium citrate: The carboxyl group of trisodium citrate is activated in the aqueous phase using a coupling agent.

[0027] S23. Surface functionalization modification of mesoporous carriers.

[0028] S231. Place the mesoporous support prepared in step S1 into a reaction vessel, add an aqueous ethanol solution with a volume ratio of ethanol to water of 7:3; heat to 55-60℃ and stir at a constant temperature.

[0029] S232. Add aminotrimethylphosphonic acid, modified sodium alginate and activated trisodium citrate in proportion, keep the reaction at a temperature for 1.5-2 hours, and uniformly graft pH-responsive functional groups onto the surface and inner wall of the mesoporous carrier through chemical bonding to form ion-gated sites.

[0030] S233. After the reaction is complete, the ethanol solvent is removed by vacuum distillation, the mixture is dried at a low temperature of 60-70℃, and then pulverized through a 2500-mesh sieve to obtain a surface-functionalized modified mesoporous support.

[0031] As the core functionalizing agent, aminotrimethylphosphonic acid contains an amino group (-NH2) and a phosphonic acid group (-PO3H2) in its molecule, which can undergo a dehydration condensation reaction with the carboxyl group (-COOH) in the activated trisodium citrate molecule to form a stable amide bond (-CONH-) and a phosphonate bond (-PO3-), while retaining the unreacted phosphonic acid group and carboxyl group to construct the basic pH response site.

[0032] The modified sodium alginate contains aldehyde (-CHO) and hydroxyl (-OH) groups, which can undergo a Schiff base reaction with the amino group (-NH2) in aminotrimethylphosphonic acid to form a -C=N- bond; and can undergo an esterification reaction with the carboxyl group (-COOH) of activated trisodium citrate to form a -COO- bond, thereby achieving covalent cross-linking of the three and forming a three-dimensional network composite functional group structure.

[0033] The composite functional groups of the mesoporous carrier contain pH-responsive groups such as carboxyl, phosphonic acid, and amino groups. These groups can achieve ion-gated functions through protonation / deprotonation transformation: when the soil pH changes, the conformation of the functional groups changes, thereby controlling the adsorption and release of nutrient ions. Moreover, the composite functional groups can be firmly grafted onto the surface of the mesoporous carrier through chemical bonding and are not easy to fall off.

[0034] By using a reaction temperature of 55-60℃ and a reaction time of 1.5-2h, aminotrimethylphosphonic acid, modified sodium alginate, and activated trisodium citrate can be reacted under relatively compatible conditions. This can promote condensation and esterification reactions while avoiding the degradation of sodium alginate and the decomposition of aminotrimethylphosphonic acid, ensuring that the three are fully cross-linked and form a stable composite functional group.

[0035] The composite functional group formed by the synergistic reaction of the three is more stable and has a higher pH response sensitivity than the functional group formed by a single modifier. It can cover different soil pH environments (acidic, neutral, and alkaline), solving the problem of narrow response range of single functional groups. The phosphonic acid group and carboxyl group in the composite functional group can combine with N, P, K and trace element ions through ionic bonds to achieve nutrient loading. At the same time, the release is controlled by pH response, which improves the slow release effect and utilization rate of fertilizer.

[0036] S3. Load nutrient raw materials into a mesoporous carrier to prepare a water-soluble fertilizer product.

[0037] This step specifically includes: S31. Mix macronutrient raw materials and micronutrient raw materials in proportion, add deionized water, heat to 45-50℃, and stir until completely dissolved to prepare a nutrient mixed aqueous solution.

[0038] S32. Slowly add the modified mesoporous support to the nutrient mixed aqueous solution and stir at a constant temperature for 40-50 minutes. Utilize the adsorption and ionic bonding of the mesoporous support to fully load nutrient ions into the pores and gating sites of the support.

[0039] S33. Add polyaspartic acid water-soluble dispersant, continue stirring for 15 minutes, and adjust the pH of the mixed solution to 6.0-7.0 with food-grade phosphoric acid.

[0040] S34. The mixed solution is fed into a spray drying tower, and the inlet air temperature is controlled at 160-180℃ and the outlet air temperature at 70-80℃. The ultrafine powder product is obtained by spray drying.

[0041] S35. After cooling, pass through a 3000-mesh sieve. After passing the inspection, seal and package to obtain slow-release water-soluble fertilizer.

[0042] The entire preparation method described above employs low-temperature operation to avoid high-temperature damage to nutrient structure and functional group activity; the spray drying parameters are set to ensure the water solubility of the finished product; and the fineness of the powder is set to ensure that the prepared water-soluble fertilizer is fully water-soluble and leaves no residue.

[0043] The present invention will now be described in further detail with reference to specific embodiments. Example 1:

[0044] A slow-release water-soluble fertilizer comprises the following raw materials in parts by weight: 30 kg of attapulgite soil mesoporous powder, 12 kg of zeolite powder, 20 kg of urea, 14 kg of potassium dihydrogen phosphate, 10 kg of potassium nitrate, 2.5 kg of EDTA chelated calcium, 1.8 kg of EDTA chelated magnesium, 0.6 kg of chelated iron, 0.4 kg of chelated zinc, 0.3 kg of chelated boron, 4 kg of trisodium citrate, 3 kg of aminotrimethylphosphonic acid, 1.2 kg of modified sodium alginate, 0.8 kg of polyaspartic acid, and 0.4 kg of food-grade phosphoric acid.

[0045] The preparation method in this embodiment is as follows: S1. Preparation of mesoporous carriers: S11. Mix attapulgite mesoporous powder and zeolite powder in a certain proportion, put them into a high-temperature activation furnace, and calcine them at 380℃ for 2.5h to remove impurities and moisture inside the minerals, broaden the pore structure, with a specific surface area ≥220m² / g and a pore size of 2-50nm, which is suitable for the construction of ion adsorption and gated channels.

[0046] S12. After calcination, the mineral is cooled to room temperature, deionized water is added at a ratio of 1:8, and the mixture is stirred for 30 minutes. After filtration, the mineral is dried and pulverized into an ultrafine powder of 2000 mesh or finer to obtain the activated mesoporous carrier.

[0047] S2. Functionalize the surface of the mesoporous carrier.

[0048] This step specifically includes: S21. Preparation of modified sodium alginate: Sodium alginate is oxidized with sodium periodate to break the vicinal diol structure on its G unit, generating aldehyde-modified sodium alginate.

[0049] S22. Activation of trisodium citrate: The carboxyl group of trisodium citrate is activated in the aqueous phase using a coupling agent.

[0050] S23. Surface functionalization modification of mesoporous carriers.

[0051] S231. Place the mesoporous support prepared in step S1 into a reaction vessel, add an aqueous ethanol solution with a volume ratio of ethanol to water of 7:3; heat to 58°C and stir at a constant temperature.

[0052] S232. Add aminotrimethylphosphonic acid, modified sodium alginate and activated trisodium citrate in proportion, keep the reaction at the temperature for 1.8h, and uniformly graft pH-responsive functional groups onto the surface and inner wall of the mesoporous carrier through chemical bonding to form ion-gated sites.

[0053] S233. After the reaction is complete, the ethanol solvent is removed by vacuum distillation, the mixture is dried at 65°C, and then pulverized through a 2500-mesh sieve to obtain a surface-functionalized modified mesoporous support.

[0054] S3. Load nutrient raw materials into a mesoporous carrier to prepare a water-soluble fertilizer product.

[0055] S31. Mix macronutrient raw materials and micronutrient raw materials in proportion, add deionized water, heat to 46°C, and stir until completely dissolved to prepare a nutrient mixed aqueous solution.

[0056] S32. Slowly add the modified mesoporous support to the nutrient mixed aqueous solution and stir at a constant temperature for 45 min. Utilize the adsorption and ionic bonding of the mesoporous support to fully load nutrient ions into the pores and gating sites of the support.

[0057] S33. Add polyaspartic acid water-soluble dispersant, continue stirring for 15 minutes, and adjust the pH of the mixed solution to 6.5 with food-grade phosphoric acid.

[0058] S34. The mixed solution is fed into a spray drying tower, and the inlet air temperature is controlled at 170°C and the outlet air temperature at 75°C. The ultrafine powder product is obtained by spray drying.

[0059] S35. After cooling, pass through a 3000-mesh sieve. After passing the inspection, seal and package to obtain 100kg of slow-release water-soluble fertilizer.

[0060] The prepared slow-release water-soluble fertilizer was subjected to performance testing: Water solubility: At 25℃, 10g of slow-release water-soluble fertilizer is dissolved in 100ml of deionized water. The dissolution is completed in 5 minutes, with no precipitate or suspended matter, and the aqueous solution is clear and transparent.

[0061] pH response performance: When the mixed solution dissolved in deionized water was applied to slightly acidic soil with pH=5.5, the nutrient release rate was 18% in 24 hours and 42% in 7 days; when applied to slightly alkaline soil with pH=7.5, the nutrient release rate was 15% in 24 hours and 38% in 7 days; when applied to neutral soil with pH=6.5, the nutrient release rate was 22% in 24 hours and 55% in 7 days, which conforms to the ion-gated slow release law.

[0062] Nutrient utilization rate: Compared with conventional water-soluble fertilizers, nitrogen utilization rate is increased by 32%, phosphorus and potassium utilization rate is increased by 28%, and nutrient leaching rate is reduced by more than 40%.

[0063] Fertilizer effect duration: After a single application, the fertilizer effect lasts for 45-50 days.

[0064] The slow-release water-soluble fertilizer prepared in this embodiment was tested for performance in the same soil environment, compared with conventional water-soluble fertilizer and traditional coated slow-release fertilizer. The results are as follows.

[0065] Water solubility conditions: 25℃, 10g / 100ml Dissolved completely in 5 minutes, with no precipitate or suspended matter. Dissolution completed in 5 minutes, with no precipitate. It is difficult to dissolve, leaves coating residue, and easily clogs the nozzle. 24-hour nutrient release rate (neutral soil) 22% More than 85% 10-15% (uniform release) 7-day cumulative release rate (neutral soil) 55% More than 98% 30-35% (uniform release) Nitrogen utilization rate (relative to conventional water-soluble fertilizers) Increased by 32% Normal level Improve by about 20% Fertilizer effect duration 45-50 days 7-10 days 40-45 days Environmental friendliness Natural biodegradable carrier, no secondary pollution, improves soil Severe nutrient leaching can easily lead to eutrophication of water bodies. The coating material is difficult to degrade and easily pollutes the soil. Adaptation mode Drip irrigation, fertigation, and foliar spraying are all suitable for fertigation. Suitable for fertigation, requiring frequent topdressing. Not compatible with drip irrigation, easily clogs pipes Example 2:

[0066] A slow-release water-soluble fertilizer comprises the following raw materials in parts by weight: 25 kg of attapulgite soil mesoporous powder, 15 kg of zeolite powder, 18 kg of urea, 15 kg of potassium dihydrogen phosphate, 12 kg of potassium nitrate, 2 kg of EDTA chelated calcium, 2 kg of EDTA chelated magnesium, 0.8 kg of chelated iron, 0.6 kg of chelated zinc, 0.6 kg of chelated boron, 3 kg of trisodium citrate, 4 kg of aminotrimethylphosphonic acid, 2 kg of modified sodium alginate, 1 kg of polyaspartic acid, and 0.5 kg of food-grade phosphoric acid.

[0067] The preparation method in this embodiment is as follows: S1. Preparation of mesoporous carriers: S11. Mix attapulgite mesoporous powder and zeolite powder in a certain proportion, put them into a high-temperature activation furnace, and calcine them at 400℃ for 2 hours to remove impurities and moisture from the minerals, broaden the pore structure, and achieve a specific surface area ≥220m² / g and a pore size of 2-50nm, which is suitable for the construction of ion adsorption and gated channels.

[0068] S12. After calcination, the mineral is cooled to room temperature, deionized water is added at a ratio of 1:8, and the mixture is stirred for 30 minutes. After filtration, the mineral is dried and pulverized into an ultrafine powder of 2000 mesh or finer to obtain the activated mesoporous carrier.

[0069] S2. Functionalize the surface of the mesoporous carrier.

[0070] This step specifically includes: S21. Preparation of modified sodium alginate: Sodium alginate is oxidized with sodium periodate to break the vicinal diol structure on its G unit, generating aldehyde-modified sodium alginate.

[0071] S22. Activation of trisodium citrate: The carboxyl group of trisodium citrate is activated in the aqueous phase using a coupling agent.

[0072] S23. Surface functionalization modification of mesoporous carriers.

[0073] S231. Place the mesoporous support prepared in step S1 into a reaction vessel, add an aqueous ethanol solution with a volume ratio of ethanol to water of 7:3; heat to 60°C and stir at a constant temperature.

[0074] S232. Add aminotrimethylphosphonic acid, modified sodium alginate and activated trisodium citrate in proportion, keep the reaction at the temperature for 1.5h, and uniformly graft pH-responsive functional groups onto the surface and inner wall of the mesoporous carrier through chemical bonding to form ion-gated sites.

[0075] S233. After the reaction is complete, the ethanol solvent is removed by vacuum distillation, the mixture is dried at 60°C, and then pulverized through a 2500-mesh sieve to obtain a surface-functionalized modified mesoporous support.

[0076] S3. Load nutrient raw materials into a mesoporous carrier to prepare a water-soluble fertilizer product.

[0077] S31. Mix macronutrient raw materials and micronutrient raw materials in proportion, add deionized water, heat to 45°C, and stir until completely dissolved to prepare a nutrient mixed aqueous solution.

[0078] S32. Slowly add the modified mesoporous support to the nutrient mixed aqueous solution and stir at a constant temperature for 50 min. Utilize the adsorption and ionic bonding of the mesoporous support to fully load nutrient ions into the pores and gating sites of the support.

[0079] S33. Add polyaspartic acid water-soluble dispersant, continue stirring for 15 minutes, and adjust the pH of the mixed solution to 6.0 with food-grade phosphoric acid.

[0080] S34. The mixed solution is fed into a spray drying tower, the inlet air temperature is controlled at 180℃ and the outlet air temperature is controlled at 80℃, and the ultrafine powder product is obtained by spray drying.

[0081] S35. After cooling, pass through a 3000-mesh sieve. After passing the inspection, seal and package to obtain 99.8 kg of slow-release water-soluble fertilizer.

[0082] The slow-release water-soluble fertilizer prepared in this embodiment is suitable for acidic soils. In acidic soils, the fertilizer release rate is slower, and the fertilizer effect period is extended to 55 days, which is suitable for the nutrient requirements of crops in acidic soils. Example 3:

[0083] A slow-release water-soluble fertilizer comprises the following raw materials in parts by weight: 35 kg of attapulgite soil mesoporous powder, 10 kg of zeolite powder, 23 kg of urea, 12 kg of potassium dihydrogen phosphate, 8 kg of potassium nitrate, 3 kg of EDTA chelated calcium, 1 kg of EDTA chelated magnesium, 0.5 kg of chelated iron, 0.3 kg of chelated zinc, 0.2 kg of chelated boron, 5 kg of trisodium citrate, 2 kg of aminotrimethylphosphonic acid, 1 kg of modified sodium alginate, 0.5 kg of polyaspartic acid, and 0.3 kg of food-grade phosphoric acid.

[0084] The preparation method in this embodiment is as follows: S1. Preparation of mesoporous carriers: S11. Mix attapulgite mesoporous powder and zeolite powder in a certain proportion, put them into a high-temperature activation furnace, and calcine them at 350℃ for 3 hours to remove impurities and moisture from the minerals, broaden the pore structure, and achieve a specific surface area ≥220m² / g and a pore size of 2-50nm, which is suitable for the construction of ion adsorption and gated channels.

[0085] S12. After calcination, the mineral is cooled to room temperature, deionized water is added at a ratio of 1:8, and the mixture is stirred for 30 minutes. After filtration, the mineral is dried and pulverized into an ultrafine powder of 2000 mesh or finer to obtain the activated mesoporous carrier.

[0086] S2. Functionalize the surface of the mesoporous carrier.

[0087] This step specifically includes: S21. Preparation of modified sodium alginate: Sodium alginate is oxidized with sodium periodate to break the vicinal diol structure on its G unit, generating aldehyde-modified sodium alginate.

[0088] S22. Activation of trisodium citrate: The carboxyl group of trisodium citrate is activated in the aqueous phase using a coupling agent.

[0089] S23. Surface functionalization modification of mesoporous carriers.

[0090] S231. Place the mesoporous support prepared in step S1 into a reaction vessel, add an aqueous ethanol solution with a volume ratio of ethanol to water of 7:3; heat to 55°C and stir at a constant temperature.

[0091] S232. Add aminotrimethylphosphonic acid, modified sodium alginate and activated trisodium citrate in proportion, keep the reaction at the temperature for 2 hours, and uniformly graft pH-responsive functional groups onto the surface and inner wall of the mesoporous carrier through chemical bonding to form ion-gated sites.

[0092] S233. After the reaction is complete, the ethanol solvent is removed by vacuum distillation, the mixture is dried at 70°C, and then pulverized through a 2500-mesh sieve to obtain a surface-functionalized modified mesoporous support.

[0093] S3. Load nutrient raw materials into a mesoporous carrier to prepare a water-soluble fertilizer product.

[0094] S31. Mix macronutrient raw materials and micronutrient raw materials in proportion, add deionized water, heat to 50°C, and stir until completely dissolved to prepare a nutrient mixed aqueous solution.

[0095] S32. Slowly add the modified mesoporous support to the nutrient mixed aqueous solution and stir at a constant temperature for 40 min. Utilize the adsorption and ionic bonding of the mesoporous support to fully load nutrient ions into the pores and gating sites of the support.

[0096] S33. Add polyaspartic acid water-soluble dispersant, continue stirring for 15 minutes, and adjust the pH of the mixed solution to 7.0 with food-grade phosphoric acid.

[0097] S34. The mixed solution is fed into a spray drying tower, and the inlet air temperature is controlled at 160°C and the outlet air temperature at 70°C. The ultrafine powder product is obtained by spray drying.

[0098] S35. After cooling, pass through a 3000-mesh sieve. After passing the inspection, seal and package to obtain 98.7 kg of slow-release water-soluble fertilizer.

[0099] The slow-release water-soluble fertilizer prepared in this embodiment is suitable for alkaline soils. In alkaline soils, the opening and closing of ion-gated channels are more sensitive, the nutrient release is more balanced, and the problem of nutrient fixation in alkaline soils is avoided.

Claims

1. A slow-release water-soluble fertilizer, characterized by comprising: The ingredients include the following parts by weight: 35-50 parts of mesoporous carrier; 6-11 parts of surface functionalizing modifier; 38-50 parts of macronutrient raw materials; 4-7 parts of trace element nutrient raw materials; 0.5-1 part of water-soluble dispersant; pH adjuster 0.3-0.5 parts.

2. The slow-release water-soluble fertilizer according to claim 1, characterized in that, The mesoporous carrier comprises the following raw materials in parts by weight: 25-35 parts of attapulgite mesoporous powder, 10-15 parts of zeolite powder, and deionized water, with a material-to-liquid ratio of 1:

8.

3. The slow-release water-soluble fertilizer according to claim 1, characterized in that, The surface functionalizing modifier comprises the following raw materials in parts by weight: 3-5 parts of trisodium citrate, 2-4 parts of aminotrimethylphosphonic acid, 1-2 parts of modified sodium alginate, and 3-5 parts of coupling agent.

4. The slow-release water-soluble fertilizer according to claim 1, characterized in that, The macronutrient raw materials include the following parts by weight: 18-23 parts urea, 12-15 parts potassium dihydrogen phosphate, and 8-12 parts potassium nitrate; the micronutrient raw materials include the following parts by weight: 2-3 parts EDTA chelated calcium, 1-2 parts EDTA chelated magnesium, 0.5-0.8 parts chelated iron, 0.3-0.6 parts chelated zinc, and 0.2-0.6 parts chelated boron.

5. A method for preparing a slow-release water-soluble fertilizer, characterized in that, The preparation of the slow-release water-soluble fertilizer according to any one of claims 1-4 specifically includes the following steps: S1. Prepare mesoporous supports with a specific surface area ≥220m² / g and a pore size of 2-50nm; S2. Functional modification of the surface of the mesoporous carrier; S3. Load nutrient raw materials into a mesoporous carrier to prepare a water-soluble fertilizer product.

6. The method for preparing a slow-release water-soluble fertilizer according to claim 5, characterized in that, Step S1 specifically includes: S11. Mix attapulgite mesoporous powder and zeolite powder in a certain proportion, put them into a high-temperature activation furnace, and calcine them at 350-400℃ for 2-3 hours to remove internal impurities and moisture from the minerals, broaden the pore structure, and increase the specific surface area. S12. After calcination, the mineral is cooled to room temperature, deionized water is added at a ratio of 1:8, and the mixture is stirred for 30 minutes. After filtration, the mineral is dried and pulverized into an ultrafine powder of 2000 mesh or finer to obtain the activated mesoporous carrier.

7. The method for preparing a slow-release water-soluble fertilizer according to claim 5, characterized in that, Step S2 specifically includes: S21. Preparation of modified sodium alginate; sodium alginate is oxidized with sodium periodate to break the vicinal diol structure on its G unit, generating aldehyde-modified sodium alginate; S22. Activation of trisodium citrate; activation of the carboxyl group of trisodium citrate in an aqueous phase using a coupling agent; S23. Surface functionalization modification of mesoporous carriers.

8. The method for preparing a slow-release water-soluble fertilizer according to claim 7, characterized in that, Step S23 specifically includes: S231. Place the mesoporous support prepared in step S1 into a reaction vessel, add an aqueous ethanol solution with a volume ratio of ethanol to water of 7:3; heat to 55-60℃ and stir at a constant temperature; S232. Add aminotrimethylphosphonic acid, modified sodium alginate and activated trisodium citrate in proportion, keep the reaction at the temperature for 1.5-2h, and uniformly graft pH-responsive functional groups onto the surface and inner wall of the mesoporous carrier through chemical bonding to form ion-gated sites. S233. After the reaction is complete, the ethanol solvent is removed by vacuum distillation, the mixture is dried at a low temperature of 60-70℃, and then pulverized through a 2500-mesh sieve to obtain a surface-functionalized modified mesoporous support.

9. The method for preparing a slow-release water-soluble fertilizer according to claim 8, characterized in that, Step S3 specifically includes: S31. Mix macronutrient raw materials and micronutrient raw materials in proportion, add deionized water, heat to 45-50℃, stir until completely dissolved, and prepare a nutrient mixed aqueous solution; S32. Slowly add the modified mesoporous support to the nutrient mixed aqueous solution and stir at a constant temperature for 40-50 minutes. Utilize the adsorption and ionic bonding of the mesoporous support to fully load nutrient ions into the pores and gating sites of the support. S33. Add water-soluble dispersant, continue stirring for 15 minutes, and adjust the pH of the mixed solution to 6.0-7.0 with pH adjuster; S34. The mixed solution is fed into a spray drying tower, the inlet air temperature is controlled at 160-180℃ and the outlet air temperature is controlled at 70-80℃, and the ultrafine powder product is obtained by spray drying. S35. After cooling, pass through a 3000-mesh sieve. After passing the inspection, seal and package to obtain slow-release water-soluble fertilizer.