Multifunctional partition controlled release compound fertilizer and preparation method thereof

Abstract

The present application relates to the technical field of fertilizer, in particular to a multifunctional zoned controlled-release mixed fertilizer and a preparation method thereof, which is prepared by physical mixing of one or any combination of the following functional particles, each of which is independently coated to realize the synergistic controlled release of multiple elements, including: controlled-release nitrogen element particles, controlled-release phosphorus element particles, controlled-release potassium element particles, controlled-release trace element particles, citric acid activated particles, and the like; the present application innovatively prepares nitrogen, phosphorus and potassium into independent controlled-release particles, each of which is coated with polyurethane, and the thickness of the coating of each particle can be flexibly adjusted according to the different requirements of crops at different growth stages for nitrogen, phosphorus and potassium, so as to realize the accurate zoned controlled release of nitrogen, phosphorus and potassium, and completely solve the core problem that the nutrient release of the existing fertilizer does not match the fertilizer requirement law of crops.

Description

Technical Field

[0002] This invention relates to the field of fertilizer technology, specifically to a multifunctional zoned controlled-release blended fertilizer and its preparation method, which is suitable for large-scale planting of grain crops, cash crops, and fruit and vegetable crops. It can achieve precise zoned controlled release of nitrogen, phosphorus, potassium and micronutrients, improve fertilizer utilization, reduce soil pollution, and take into account both high yield and ecological environmental protection needs. Background Technology

[0004] With the advancement of agricultural modernization, traditional fertilizers suffer from problems such as a mismatch between nutrient release rate and crop nutrient requirements, low nutrient utilization, and a tendency to cause soil compaction and eutrophication, making them unable to meet the development needs of high-quality and efficient agriculture. Controlled-release fertilizers, as a new type of fertilizer, regulate nutrient release rates through coating technology, which can solve the above problems to some extent, but existing controlled-release fertilizers still have many shortcomings.

[0005] Currently, most controlled-release blended fertilizers on the market employ two unreasonable designs: one is to coat all macronutrients such as nitrogen, phosphorus, and potassium together, and the other is to coat only the mixed macronutrient particles and micronutrient particles separately. Both designs result in the inability to independently regulate the release rates of nitrogen, phosphorus, and potassium. Because the nitrogen, phosphorus, and potassium requirements of crops vary significantly at different growth stages (for example, high nitrogen requirements and moderate phosphorus and potassium requirements during the seedling stage, a surge in phosphorus and potassium requirements and stable nitrogen requirements during the flowering stage, and high potassium requirements and declining nitrogen and phosphorus requirements during the grain-filling stage), existing designs cannot adapt to these differentiated nutrient requirements, easily leading to nutrient waste or crop deficiencies.

[0006] Meanwhile, in existing controlled-release fertilizers, micronutrients mostly exist in the form of inorganic salts, which are easily fixed in the soil, have low solubility, and poor crop absorption and utilization. Some fertilizers add citric acid to activate micronutrients, but when citric acid is mixed with macronutrients, it undergoes a complexation reaction with phosphorus, forming insoluble precipitates and reducing phosphorus availability, thus affecting the overall fertilizer efficiency. Furthermore, the coating materials of existing controlled-release fertilizers often suffer from poor stability, excessively fast or slow degradation rates, and high costs. Moreover, the preparation processes have not been optimized for separate coatings of nitrogen, phosphorus, and potassium, making large-scale production difficult.

[0007] Therefore, developing a multifunctional controlled-release blended fertilizer that can achieve separate zoned controlled release of nitrogen, phosphorus, and potassium, take into account the activation of trace elements and synergistic nutrient supply, avoid antagonistic effects between nutrients, and has a simple preparation process and controllable cost has become an urgent technical problem to be solved in the fertilizer field. Summary of the Invention

[0009] To address the aforementioned deficiencies in existing technologies, the present invention aims to provide a multifunctional zoned controlled-release blended fertilizer and its preparation method. By separately coating nitrogen, phosphorus, and potassium from the macroelements, and then physically blending them with controlled-release trace element particles and citric acid activated particles, the independent and precise controlled release of nitrogen, phosphorus, potassium, and microelements is achieved. This solves problems such as asynchronous release of nitrogen, phosphorus, and potassium, easy fixation of trace elements, nutrient antagonism, and unstable fertilizer efficiency, thereby improving fertilizer utilization, reducing agricultural non-point source pollution, simplifying the preparation process, reducing production costs, and meeting the needs of large-scale agricultural production.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A multifunctional zoned controlled-release blended fertilizer, characterized in that it is formed by physically blending one or any combination of the following functional particles, each of which is independently coated to achieve synergistic controlled release of multiple elements, including:

[0012] Controlled-release nitrogen particles: comprising a nitrogen nutrient core and a first polyurethane coating layer covering the surface of the nitrogen nutrient core, wherein the nitrogen nutrient core is made from at least one of urea, ammonium chloride, and ammonium nitrate; further, the first polyurethane coating layer is a modified polyurethane coating layer, wherein 5%-10% by mass of a pH-sensitive monomer (2-acrylamide-2-methylpropanesulfonic acid) and 3%-5% by mass of a temperature-sensitive monomer (N-isopropylacrylamide) are added to its raw materials, which can dynamically adjust the nitrogen release rate according to changes in soil pH and temperature, adapting to different soil environments and temperature changes during crop growth stages.

[0013] Controlled-release phosphorus particles: comprising a phosphorus nutrient core and a second polyurethane coating layer covering the surface of the phosphorus nutrient core, wherein the phosphorus nutrient core is made from at least one of monoammonium phosphate and diammonium phosphate; furthermore, the second polyurethane coating layer is a porous modified coating layer, the surface of which has air and water permeable pores with a pore size of 1-5 μm, and the pore walls are coated with a phosphate ion adsorption layer (made of hydroxyapatite powder), which can reduce the binding of phosphorus with calcium and magnesium ions in the soil, reduce phosphorus fixation, and at the same time achieve slow release of phosphorus through the porous structure, which is suitable for the phosphorus needs of crops in the middle and late stages.

[0014] Controlled-release potassium granules: comprising a potassium nutrient core and a third polyurethane coating layer covering the surface of the potassium nutrient core, wherein the potassium nutrient core is made from at least one of potassium chloride and potassium sulfate; furthermore, the third polyurethane coating layer contains 4%-8% by mass of a potassium ion channel regulator (potassium alginate), which can promote the permeation and release of potassium ions from the coating layer, while inhibiting the leaching and loss of potassium ions in the soil, thereby improving the utilization rate of potassium, especially suitable for the rapid supply of potassium during the grain-filling and ripening stages of crops.

[0015] Controlled-release micronutrient particles: comprising a micronutrient core and a fourth polyurethane coating layer covering the surface of the micronutrient core, wherein the micronutrient core contains at least one micronutrient; furthermore, the fourth polyurethane coating layer contains 2%-4% by mass of a biostimulant (humic acid), which can promote crop root growth, enhance the crop's ability to absorb micronutrients, and improve the soil microecological environment.

[0016] Citric acid activated granules: comprising citric acid and a carrier, wherein the citric acid activated granules are either fast-release or controlled-release, and the controlled-release citric acid activated granules are coated with a fifth polyurethane coating layer. Furthermore, the carrier is a modified composite carrier, made by mixing diatomaceous earth, bentonite, and zeolite powder in a mass ratio of 3:2:1, followed by high-temperature activation (500-600℃). The activated carrier has a specific surface area increased by more than 30%, significantly enhanced adsorption performance, and can achieve slow release of citric acid, prolonging the activation time, while further improving the soil's water and fertilizer retention capacity.

[0017] Furthermore, the surface of the trace element nutrient core of the controlled-release trace element particles is also provided with a citric acid chelation treatment layer, which is formed by spraying a citric acid solution onto the dried trace element nutrient core. The citric acid chelation treatment layer can convert trace elements into a chelated state, significantly improving their stability and solubility in the soil, preventing them from being fixed by soil colloids, and simultaneously promoting the absorption of trace elements by crop roots, thus solving the problem of low trace element utilization in existing technologies.

[0018] Furthermore, the controlled-release trace element particles contain 1%-2% by mass of disodium EDTA in the citric acid chelation treatment layer. This disodium EDTA can form a synergistic chelation effect with citric acid, further enhancing the chelation stability of the trace elements and preventing them from being fixed in the soil. At the same time, it promotes the absorption of chelated trace elements by crop roots, solving the problem of low trace element utilization in existing technologies. The thickness of the chelation treatment layer is 10-20 μm, ensuring the chelation effect without affecting the adhesion stability of the subsequent coating layer.

[0019] Furthermore, the nutrient cores of the controlled-release nitrogen, phosphorus, and potassium particles do not contain citric acid; independent controlled release is achieved solely through their respective polyurethane coating layers. This design effectively prevents the complexation reaction between citric acid and phosphorus, thus preventing the formation of insoluble precipitates and ensuring the availability of phosphorus. Simultaneously, it avoids interference from citric acid on the controlled-release rates of nitrogen and potassium, achieving precise controlled release of each nutrient and adapting to the differentiated nutrient requirements of crops at different growth stages.

[0020] Furthermore, all three types of controlled-release granules contain 1%-3% by mass of antioxidant (di-tert-butyl-p-cresol) in their coating layers, which can prevent the coating material from oxidizing and degrading too quickly in the soil, ensuring that the controlled-release cycle is precisely matched with the crop growth period (the controlled-release cycle can be adjusted to 30-120 days depending on the coating thickness), thus solving the problem of unstable degradation rate of existing coating materials.

[0021] Furthermore, the micronutrients are selected from at least one of zinc, magnesium, copper, manganese, and boron. Specifically, raw materials such as zinc sulfate, magnesium sulfate, copper sulfate, manganese sulfate, and boric acid can be used. These are all essential micronutrients for crop growth. The specific types and contents can be adjusted according to the crop type and soil nutrient status. For example, fruit and vegetable crops require a higher amount of boron, so the proportion of boron can be appropriately increased; grain crops require a higher amount of zinc and manganese, so adjustments can be made accordingly.

[0022] Furthermore, in the citric acid activated particles, the mass fraction of citric acid is 10%-30%, and the carrier is at least one of diatomaceous earth, bentonite, and zeolite powder. Controlling the mass fraction of citric acid at 10%-30% ensures its activation effect on fixed nutrients in the soil while avoiding excessive use that could lead to an excessive decrease in soil pH. The carrier, made of natural mineral materials such as diatomaceous earth, bentonite, and zeolite powder, has the characteristics of large specific surface area and strong adsorption, which can adsorb citric acid and release it slowly, prolonging its activation time and reducing citric acid loss. In addition, this type of carrier is widely available, inexpensive, and can also improve soil structure and enhance soil water and fertilizer retention capacity.

[0023] Furthermore, the particle size of the controlled-release nitrogen particles, controlled-release phosphorus particles, controlled-release potassium particles, controlled-release trace element particles, and citric acid-activated particles are all 1-4 mm; the thickness of the first, second, third, fourth, and fifth polyurethane coating layers is all 50-200 μm. Controlling the particle size to 1-4 mm ensures uniform mixing of the five functional particles during blending and facilitates full contact with the soil during sowing, avoiding uneven nutrient release due to excessively large particles. The coating thickness of 50-200 μm can be flexibly adjusted according to the release requirements of nitrogen, phosphorus, potassium, and trace elements (for example, a thinner coating of 50-100 μm can be used for nitrogen, which needs rapid release during the seedling stage, while a thicker coating of 100-200 μm can be used for phosphorus and potassium, which need slow release in the mid-to-late stages). The polyurethane coating material has the characteristics of good stability, controllable degradation rate, and non-toxicity and environmental friendliness, and can gradually degrade during the crop growth period without causing soil pollution.

[0024] Furthermore, the mixing mass ratio of controlled-release nitrogen granules, controlled-release phosphorus granules, controlled-release potassium granules, controlled-release micronutrient granules, and citric acid activated granules is (30-45):(15-25):(10-20):(10-20):(5-15). This ratio has been verified through extensive experiments and can achieve the synergistic effect of nitrogen, phosphorus, potassium, micronutrients, and citric acid activator, ensuring that the nutrient requirements of crops at different growth stages are precisely met: controlled-release nitrogen granules account for 30-45%, providing a basic nitrogen source for crop growth and meeting the nitrogen requirements from seedling to maturity; controlled-release phosphorus granules account for 15-25%, meeting the phosphorus requirements for crop root growth, flowering, pollination, and grain development; controlled-release potassium granules account for 10-20%, enhancing crop stress resistance and meeting the potassium requirements during the grain-filling and maturity stages; controlled-release micronutrient granules account for... The proportion of citric acid activated granules is 10-20%, which supplements the micronutrients needed for crop growth and avoids deficiency symptoms; the proportion of citric acid activated granules is 5-15%, which can activate fixed phosphorus and micronutrients in the soil, improve the overall utilization rate of fertilizer, and at the same time regulate soil pH and improve the soil environment; furthermore, the mixing ratio can be adjusted according to different soil types (acidic, alkaline, neutral). For example, the proportion of citric acid activated granules can be appropriately increased in acidic soil (12-15%), and the proportion of controlled-release phosphorus granules can be appropriately increased in alkaline soil (22-25%) to improve the soil adaptability of fertilizer.

[0025] This invention also provides a method for preparing the above-mentioned multifunctional zoned controlled-release blended fertilizer, characterized by comprising the following steps:

[0026] S1. Preparation of controlled-release nitrogen element particles: Nitrogen element raw materials are mixed evenly with a carrier, granulated and dried, and then coated with a polyurethane coating agent to obtain controlled-release nitrogen element particles.

[0027] Furthermore, the nitrogen raw material is mixed evenly with the carrier, granulated, dried, and then coated with a modified polyurethane coating agent to obtain controlled-release nitrogen particles. The modified polyurethane coating agent is prepared by mixing polyurethane resin, pH-sensitive monomer, temperature-sensitive monomer, and antioxidant in a mass ratio of 82-91:5-10:3-5:1-3, adding an appropriate amount of organic solvent (acetone), stirring evenly, heating to 50-60℃ for 30-40 minutes, cooling to room temperature, and then storing for later use. This coating agent can achieve environmentally adaptive controlled release.

[0028] S2. Preparation of controlled-release phosphorus particles: The phosphorus raw material is mixed evenly with the carrier, granulated and dried, and then coated with a polyurethane coating agent to obtain controlled-release phosphorus particles.

[0029] Furthermore, the phosphorus raw material is mixed evenly with the carrier, granulated, and dried, and then coated with a porous modified polyurethane coating agent to obtain controlled-release phosphorus particles. The preparation method of the porous modified polyurethane coating agent is as follows: polyurethane resin, hydroxyapatite powder, and antioxidant are mixed in a mass ratio of 89-95:3-5:1-3, an appropriate amount of foaming agent (sodium bicarbonate) is added, and after stirring evenly, a fluidized bed coating process is adopted. During the coating process, the temperature (45-55℃) and wind speed are controlled to form 1-5μm air and water permeable pores in the coating layer, so as to realize the slow release and anti-fixation of phosphorus.

[0030] S3. Preparation of controlled-release potassium element particles: The potassium element raw material is mixed evenly with the carrier, granulated and dried, and then coated with a polyurethane coating agent to obtain controlled-release potassium element particles.

[0031] Furthermore, the potassium element raw material is mixed evenly with the carrier, granulated, and dried, and then coated with a polyurethane coating agent containing a potassium ion channel modifier to obtain controlled-release potassium element particles. The coating agent is prepared by mixing polyurethane resin, potassium alginate, and antioxidant in a mass ratio of 89-94:4-8:1-3, adding an appropriate amount of organic solvent, stirring evenly, and then setting it aside. This can promote the permeation and release of potassium ions and inhibit leaching loss.

[0032] S4. Preparation of controlled-release trace element particles: The trace element raw materials are mixed evenly with the carrier, granulated and dried, and then sprayed with citric acid solution for surface chelation treatment. After drying again, polyurethane coating agent is used for coating treatment to obtain controlled-release trace element particles.

[0033] Furthermore, the trace element raw materials are mixed evenly with the carrier, granulated, and dried. A citric acid-EDTA disodium mixed solution is then sprayed onto the surface for chelation treatment. After drying again, a polyurethane coating agent containing biostimulants is used for coating treatment to obtain controlled-release trace element particles. The mass concentration of the citric acid-EDTA disodium mixed solution is 5%-15%, with a mass ratio of citric acid to EDTA disodium of 8:2. The spraying amount is 3%-8% of the mass of the trace element nutrient core. The polyurethane coating agent containing biostimulants is prepared by mixing polyurethane resin, humic acid, and antioxidant in a mass ratio of 93-97:2-4:1-3, stirring evenly, and then storing for later use. This process can promote crop root growth and improve the absorption efficiency of trace elements.

[0034] S5. Preparation of citric acid activated granules: Citric acid and carrier are mixed evenly, granulated and dried to obtain immediate-release citric acid activated granules; or granulated and dried, and then coated with a polyurethane coating agent to obtain controlled-release citric acid activated granules.

[0035] Furthermore, citric acid is mixed evenly with the modified composite carrier, granulated, and dried to obtain immediate-release citric acid activated particles; or, after granulation and drying, polyurethane coating agent is used for coating treatment to obtain controlled-release citric acid activated particles. The modified composite carrier is prepared by mixing diatomaceous earth, bentonite, and zeolite powder in a mass ratio of 3:2:1, placing them in a muffle furnace, activating them at 500-600℃ for 2-3 hours, cooling to room temperature, and then pulverizing them to 80-100 mesh for later use. Its adsorption performance is significantly improved compared to the unactivated carrier.

[0036] S6. Blending: Mix the five functional granules obtained in steps S1 to S5 evenly according to a preset mass ratio to obtain a multifunctional zoned controlled-release blended fertilizer.

[0037] Furthermore, the five functional granules obtained in steps S1 to S5 are mixed evenly according to a preset mass ratio, and 0.1%-0.3% by mass of an anti-caking agent (silica) is added. After stirring evenly, the mixture is sieved, measured, and packaged to obtain a multifunctional zoned controlled-release blended fertilizer. The anti-caking agent can prevent the granules from clumping during storage and transportation, ensuring fertilizer uniformity and solving the technical problem of easy clumping in existing blended fertilizers.

[0038] Further, in steps S1 to S5, the granulation temperature is 60-80℃, the drying temperature is 80-100℃, and the particles are dried until the moisture content is ≤2%. The coating treatment adopts a fluidized bed coating process, and the coating temperature is 40-60℃. Controlling the granulation temperature at 60-80℃ ensures that the raw materials are fully integrated, forming a uniform particle core with moderate strength. Controlling the drying temperature at 80-100℃ quickly removes moisture from the particles, ensuring a moisture content of ≤2%, and preventing excessive moisture from causing particle agglomeration and coating layer detachment. The fluidized bed coating process features uniform coating, high efficiency, and low energy consumption, making it suitable for large-scale production. Controlling the coating temperature at 40-60℃ ensures that the polyurethane coating agent is uniformly adhered to the surface of each particle, forming a stable coating layer, while avoiding excessive temperature from causing coating agent degradation and nutrient loss.

[0039] Furthermore, in step S4, the citric acid solution has a mass concentration of 5%-15%, and the spraying amount is 3%-8% of the mass of the trace element nutrient core. The drying temperature after spraying is 70-90℃, and the drying time is 15-30 minutes. The optimized mass concentration and spraying amount of the citric acid solution ensure the formation of a uniform chelated treatment layer on the surface of the trace element core, guaranteeing the chelation effect while avoiding excessive citric acid leading to increased costs. Controlling the drying temperature and time after spraying ensures that the citric acid and trace elements undergo a sufficient chelation reaction, while removing excess moisture to avoid affecting the subsequent coating effect.

[0040] By adopting the above technical solution, the present invention has the following beneficial effects:

[0041] 1. Nitrogen, phosphorus, and potassium are individually coated, overcoming the core limitations of existing mixed coatings: Current controlled-release blended fertilizers do not achieve individual coating of nitrogen, phosphorus, and potassium. They either mix and coat all three or only coat the macro-elements and micro-elements separately, failing to achieve independent controlled release of nitrogen, phosphorus, and potassium. This invention innovatively formulates nitrogen, phosphorus, and potassium into separate controlled-release granules, each coated with polyurethane. The coating thickness of each granule can be flexibly adjusted according to the differentiated nitrogen, phosphorus, and potassium requirements of crops at different growth stages, achieving precise zoned controlled release of nitrogen, phosphorus, and potassium. This completely solves the core problem of the mismatch between nutrient release from existing fertilizers and crop nutrient requirements.

[0042] 2. Multi-particle synergistic design solves the dual problems of nutrient antagonism and low utilization rate of trace elements: In the prior art, when citric acid is mixed with macronutrients, it will react with phosphorus to form an insoluble precipitate, reducing the utilization rate of phosphorus. The present invention prepares citric acid into citric acid activated particles separately, and the core of the nitrogen, phosphorus, and potassium controlled-release particles does not contain citric acid. At the same time, a citric acid chelation treatment layer is set on the surface of the controlled-release trace element particles. This not only realizes the chelation and activation of trace elements by citric acid, improving their absorption and utilization rate, but also avoids the antagonistic reaction between citric acid and phosphorus, ensuring the effectiveness of nitrogen, phosphorus, potassium and trace elements. This design has not been disclosed or implied in the prior art and has significant inventiveness.

[0043] 3. Synergistic effect of all elements to improve the overall performance of fertilizer: This invention achieves the synergistic effect of "separate controlled release of nitrogen, phosphorus and potassium + chelation and activation of trace elements + soil improvement" through the scientific ratio of five functional particles: controlled-release nitrogen, phosphorus and potassium particles stably supply their respective nutrients to meet the needs of crops at different growth stages; controlled-release trace element particles provide chelated trace elements to reduce soil fixation; citric acid activation particles activate soil fixed nutrients and regulate soil pH. The combination of these three not only improves fertilizer utilization but also improves soil structure and reduces soil pollution. Compared with existing single-function controlled-release fertilizers, it has significant technical advantages.

[0044] 4. Optimized preparation process, suitable for large-scale production: This invention addresses the core requirement of separate coating of nitrogen, phosphorus, and potassium by optimizing the fluidized bed coating process, simplifying the preparation process, reducing energy consumption and production costs. At the same time, by precisely controlling the temperature and parameters of granulation, drying, and coating, the quality of the five functional granules is ensured to be stable, solving the problems of complex preparation processes, high costs, and difficulty in large-scale production of existing controlled-release fertilizers. Attached Figure Description

[0046] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0047] Figure 1 This is a comparison chart of nutrient controlled-release periods provided in an embodiment of the present invention;

[0048] Figure 2 A comparison chart showing the production improvement effect provided in the embodiments of the present invention. Detailed Implementation

[0050] The following will be combined with the appendix Figure 1 and Figure 2 As shown, the technical solution of the present invention is clearly and completely described. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0052] Example 1:

[0053] A multifunctional zoned controlled-release blended fertilizer is composed of controlled-release nitrogen granules, controlled-release phosphorus granules, controlled-release potassium granules, controlled-release trace element granules, and fast-release citric acid activated granules in a mass ratio of 40:20:15:15:10.

[0054] Among them, the controlled-release nitrogen particles have the following characteristics: the nitrogen nutrient core is urea (purity ≥98%), the carrier is bentonite (addition amount is 5% of urea quality); the thickness of the first polyurethane coating layer is 80μm; and the particle size is 2-3mm.

[0055] Controlled-release phosphorus particles: The phosphorus nutrient core is monoammonium phosphate (phosphorus content ≥46%), the carrier is diatomaceous earth (added at 6% of the mass of monoammonium phosphate); the thickness of the second polyurethane coating layer is 120μm; the particle size is 2-3mm.

[0056] Controlled-release potassium particles: The potassium nutrient core is potassium chloride (potassium content ≥60%), the carrier is zeolite powder (added at 4% of the mass of potassium chloride); the thickness of the third polyurethane coating layer is 100μm; the particle size is 2-3mm.

[0057] Controlled-release trace element particles: The trace element nutrient core is composed of zinc sulfate, magnesium sulfate, and boric acid mixed in a mass ratio of 50:30:20, and the carrier is diatomaceous earth (added at 8% of the total mass of the trace element raw materials); the citric acid chelation treatment layer is sprayed with a 10% citric acid solution, and the spraying amount is 5% of the mass of the trace element nutrient core; the fourth polyurethane coating layer has a thickness of 80μm; the particle size is 2-3mm.

[0058] Immediate-release citric acid activated granules: citric acid mass fraction is 20%, carrier is zeolite powder (mass fraction 80%); particle size is 2-3mm.

[0059] The preparation method is as follows:

[0060] S1. Preparation of controlled-release nitrogen particles: Urea and bentonite are mixed evenly and granulated at 65℃. Then, the granules are dried at 90℃ until the moisture content is ≤2%. The controlled-release nitrogen particles are obtained by using a fluidized bed coating process and coating with a polyurethane coating agent at 50℃ to a coating thickness of 80μm.

[0061] S2. Preparation of controlled-release phosphorus particles: Monoammonium phosphate and diatomaceous earth are mixed evenly and granulated at 70°C. Then, the granules are dried at 95°C until the moisture content is ≤2%. The controlled-release phosphorus particles are obtained by using a fluidized bed coating process and coating with a polyurethane coating agent at 55°C to a coating thickness of 120μm.

[0062] S3. Preparation of controlled-release potassium element particles: Potassium chloride and zeolite powder are mixed evenly, granulated at 68℃, and then dried at 92℃ until the particle moisture content is ≤2%. The particles are coated with polyurethane coating agent at 48℃ using a fluidized bed coating process, with a coating thickness of 100μm, to obtain controlled-release potassium element particles.

[0063] S4. Preparation of controlled-release trace element particles: Zinc sulfate, magnesium sulfate, boric acid and diatomaceous earth are mixed evenly, granulated at 70℃, dried at 95℃ until the particle moisture content is ≤2%, then sprayed with a 10% citric acid solution (the spraying amount is 5% of the core mass), dried at 80℃ for 20 min, and then coated with a polyurethane coating agent at 45℃ using a fluidized bed coating process, with a coating thickness of 80μm, to obtain controlled-release trace element particles.

[0064] S5. Preparation of immediate-release citric acid activated granules: Citric acid and zeolite powder are mixed evenly, granulated at 75°C, and dried at 85°C until the moisture content of the granules is ≤2% to obtain immediate-release citric acid activated granules.

[0065] S6. Blending: Mix the five types of granules obtained in steps S1-S5 evenly in a mass ratio of 40:20:15:15:10 to obtain a multifunctional zoned controlled-release blended fertilizer.

[0066] Technical effects:

[0067] The fertilizer prepared in this embodiment achieves synergistic controlled and rapid release of nitrogen, phosphorus, potassium, and trace elements. The rapid-release citric acid-activated granules quickly release citric acid, regulating soil pH and promoting the activation of fixed phosphorus, potassium, and trace elements in the soil, thus improving nutrient utilization. The coating thickness of each controlled-release granule is matched to the carrier, with a controlled-release period of 60-70 days for nitrogen, 80-90 days for phosphorus, 70-80 days for potassium, and 60-70 days for trace elements, meeting the nutrient requirements of crops throughout their entire growth cycle. Field trials show that compared to ordinary blended fertilizers, this fertilizer can increase wheat yield by 8.5%-10.2%, improve nutrient utilization by 12%-15%, and increase soil organic matter content by 3.8%-4.5%, effectively improving soil compaction.

[0068] Example 2:

[0069] A multifunctional zoned controlled-release blended fertilizer is composed of controlled-release nitrogen granules, controlled-release phosphorus granules, controlled-release potassium granules, controlled-release trace element granules, and controlled-release citric acid activated granules in a mass ratio of 45:15:15:10:15.

[0070] Among them, the controlled-release nitrogen particles have the following characteristics: the nitrogen nutrient core is ammonium nitrate (nitrogen content ≥34%), the carrier is zeolite powder (added at 6% of the mass of ammonium nitrate); the thickness of the first polyurethane coating layer is 70μm; and the particle size is 1-2mm.

[0071] Controlled-release phosphorus particles: The phosphorus nutrient core is diammonium phosphate (phosphorus content ≥48%), the carrier is bentonite (added at 5% of the mass of diammonium phosphate); the thickness of the second polyurethane coating layer is 150μm; the particle size is 1-2mm.

[0072] Controlled-release potassium particles: The potassium nutrient core is potassium sulfate (potassium content ≥50%), the carrier is diatomaceous earth (added at 5% of the mass of potassium sulfate); the thickness of the third polyurethane coating layer is 120μm; the particle size is 1-2mm.

[0073] Controlled-release trace element particles: The trace element nutrient core is composed of copper sulfate, manganese sulfate, and boric acid in a mass ratio of 40:40:20, and the carrier is bentonite (added at 6% of the total mass of the trace element raw materials); the citric acid chelation treatment layer is sprayed with a 15% citric acid solution, and the spraying amount is 3% of the mass of the trace element nutrient core; the fourth polyurethane coating layer has a thickness of 120μm; the particle size is 1-2mm.

[0074] Controlled-release citric acid activated particles: citric acid mass fraction is 30%, diatomaceous earth (mass fraction 70%) is the carrier; the fifth polyurethane coating layer has a thickness of 50μm; the particle size is 1-2mm.

[0075] The preparation method is as follows:

[0076] S1. Preparation of controlled-release nitrogen particles: Ammonium nitrate and zeolite powder are mixed evenly, granulated at 75℃, and then dried at 100℃ until the particle moisture content is ≤2%. The particles are coated with a polyurethane coating agent at 60℃ using a fluidized bed coating process, with a coating thickness of 70μm, to obtain controlled-release nitrogen particles.

[0077] S2. Preparation of controlled-release phosphorus particles: Diammonium phosphate and bentonite are mixed evenly and granulated at 72°C. Then, the particles are dried at 98°C until the moisture content is ≤2%. The particles are coated with a polyurethane coating agent at 58°C using a fluidized bed coating process, with a coating thickness of 150μm, to obtain controlled-release phosphorus particles.

[0078] S3. Preparation of controlled-release potassium particles: Potassium sulfate and diatomaceous earth are mixed evenly and granulated at 70°C. Then, the granules are dried at 96°C until the moisture content is ≤2%. The controlled-release potassium particles are obtained by coating with a polyurethane coating agent at 52°C using a fluidized bed coating process, with a coating thickness of 120μm.

[0079] S4. Preparation of controlled-release trace element particles: Copper sulfate, manganese sulfate, boric acid and bentonite are mixed evenly, granulated at 80℃, dried at 100℃ until the particle moisture content is ≤2%, then sprayed with a 15% citric acid solution (the spraying amount is 3% of the core mass), dried at 90℃ for 15 min, and then coated with a polyurethane coating agent at 55℃ using a fluidized bed coating process, with a coating thickness of 120μm, to obtain controlled-release trace element particles.

[0080] S5. Preparation of controlled-release citric acid activated granules: Citric acid and diatomaceous earth are mixed evenly, granulated at 80℃, and dried at 90℃ until the moisture content of the granules is ≤2%. Then, a fluidized bed coating process is used to coat the granules with a polyurethane coating agent at 40℃, with a coating thickness of 50μm, to obtain controlled-release citric acid activated granules.

[0081] S6. Blending: Mix the five types of granules obtained in steps S1-S5 evenly in a mass ratio of 45:15:15:10:15 to obtain a multifunctional zoned controlled-release blended fertilizer.

[0082] Technical effects:

[0083] This embodiment uses controlled-release citric acid activating granules, with a 50μm polyurethane coating to achieve slow release of citric acid, preventing rapid loss and extending the soil activation cycle. An ammonium nitrate core combined with a zeolite powder carrier enhances nitrogen stability and reduces nitrogen volatilization loss. Diammonium phosphate combined with a bentonite carrier enhances phosphorus adsorption in the soil and reduces phosphorus fixation. This fertilizer has a controlled-release period of 55-65 days for nitrogen, 90-100 days for phosphorus, 80-90 days for potassium, and 70-80 days for micronutrients. When applied to corn cultivation, it increases corn yield by 9.3%-11.5%, nitrogen utilization rate by 14%-16%, and micronutrient content in corn kernels by 5.2%-6.8%, effectively improving corn quality.

[0084] Example 3:

[0085] A multifunctional zoned controlled-release blended fertilizer is composed of controlled-release nitrogen granules, controlled-release phosphorus granules, controlled-release potassium granules, controlled-release trace element granules, and fast-release citric acid activated granules in a mass ratio of 30:25:20:20:5.

[0086] Among them, the controlled-release nitrogen particles have the following characteristics: the nitrogen nutrient core is ammonium chloride (nitrogen content ≥25%), the carrier is diatomaceous earth (added at 4% of the mass of ammonium chloride); the thickness of the first polyurethane coating layer is 100μm; and the particle size is 3-4mm.

[0087] Controlled-release phosphorus particles: The phosphorus nutrient core is monoammonium phosphate (phosphorus content ≥46%), the carrier is zeolite powder (added at 7% of the mass of monoammonium phosphate); the thickness of the second polyurethane coating layer is 110μm; the particle size is 3-4mm.

[0088] Controlled-release potassium particles: The potassium nutrient core is potassium chloride (potassium content ≥60%), the carrier is bentonite (added at 6% of the mass of potassium chloride); the thickness of the third polyurethane coating layer is 90μm; the particle size is 3-4mm.

[0089] Controlled-release trace element particles: The trace element nutrient core is composed of zinc sulfate, manganese sulfate, and magnesium sulfate mixed in a mass ratio of 30:30:40, and the carrier is zeolite powder (added at 10% of the total mass of the trace element raw materials); the citric acid chelation treatment layer is sprayed with a 5% citric acid solution, and the spraying amount is 8% of the mass of the trace element nutrient core; the fourth polyurethane coating layer has a thickness of 100μm; the particle size is 3-4mm.

[0090] Immediate-release citric acid activated granules: citric acid mass fraction is 10%, and the carrier is bentonite (mass fraction 90%); the particle size is 3-4 mm.

[0091] The preparation method is as follows:

[0092] S1. Preparation of controlled-release nitrogen particles: Ammonium chloride and diatomaceous earth are mixed evenly and granulated at 60°C. Then, the particles are dried at 80°C until the moisture content is ≤2%. The particles are coated with a polyurethane coating agent at 40°C using a fluidized bed coating process, with a coating thickness of 100μm, to obtain controlled-release nitrogen particles.

[0093] S2. Preparation of controlled-release phosphorus particles: Monoammonium phosphate and zeolite powder are mixed evenly and granulated at 65°C. Then, the granules are dried at 88°C until the moisture content is ≤2%. The controlled-release phosphorus particles are obtained by coating with polyurethane coating agent at 45°C using a fluidized bed coating process, with a coating thickness of 110μm.

[0094] S3. Preparation of controlled-release potassium particles: Potassium chloride and bentonite are mixed evenly and granulated at 62℃. Then, the particles are dried at 85℃ until the moisture content is ≤2%. The particles are coated with a polyurethane coating agent at 42℃ using a fluidized bed coating process, with a coating thickness of 90μm, to obtain controlled-release potassium particles.

[0095] S4. Preparation of controlled-release trace element particles: Zinc sulfate, manganese sulfate, magnesium sulfate and zeolite powder are mixed evenly, granulated at 65℃, dried at 85℃ until the particle moisture content is ≤2%, then sprayed with a 5% citric acid solution (spraying amount is 8% of the core mass), dried at 70℃ for 30 min, and then coated with a polyurethane coating agent at 50℃ using a fluidized bed coating process, with a coating thickness of 100μm, to obtain controlled-release trace element particles.

[0096] S5. Preparation of immediate-release citric acid activated granules: Citric acid and bentonite are mixed evenly, granulated at 65℃, and dried at 80℃ until the moisture content of the granules is ≤2% to obtain immediate-release citric acid activated granules.

[0097] S6. Blending: Mix the five types of granules obtained in steps S1-S5 evenly in a mass ratio of 30:25:20:20:5 to obtain a multifunctional zoned controlled-release blended fertilizer.

[0098] Technical effects:

[0099] This embodiment optimizes the particle size (3-4 mm) of each particle, improving fertilizer dispersion in the soil and preventing excessively high local nutrient concentrations. The ammonium chloride core, combined with a diatomaceous earth carrier, is suitable for saline-alkali soil environments, reducing soil salinity and minimizing chloride ion damage to crops. The increased magnesium sulfate proportion in the micronutrient core, along with increased citric acid spraying, further enhances the chelation efficiency and activation effect of micronutrients. This fertilizer has a controlled-release period of 70-80 days for nitrogen, 85-95 days for phosphorus, 75-85 days for potassium, and 75-85 days for micronutrients. When applied to cotton cultivation, it increases cotton yield by 7.8%-9.5%, fiber length by 2.3%-3.1%, and reduces soil salinity by 4.2%-5.0%, significantly improving planting conditions in saline-alkali soils.

[0100] Example 4:

[0101] A multifunctional zoned controlled-release blended fertilizer is composed of controlled-release nitrogen granules, controlled-release phosphorus granules, controlled-release potassium granules, controlled-release trace element granules, and fast-release citric acid activated granules in a mass ratio of 40:20:15:15:10, with an anti-caking agent (silica) of 0.2% by mass added.

[0102] Among them, the controlled-release nitrogen particles have the following characteristics: the nitrogen nutrient core is urea (purity ≥98%), and the carrier is bentonite (added at 5% of the urea quality); the first polyurethane coating layer is a modified polyurethane coating layer with a thickness of 80μm, and the coating agent is made by mixing polyurethane resin, 2-acrylamide-2-methylpropanesulfonic acid, N-isopropylacrylamide, and di-tert-butyl-p-cresol in a mass ratio of 85:7:5:3; the particle size is 2-3mm.

[0103] Controlled-release phosphorus particles: The phosphorus nutrient core is monoammonium phosphate (phosphorus content ≥46%), and the carrier is diatomaceous earth (added at 6% of the mass of monoammonium phosphate); the second polyurethane coating layer is a porous modified coating layer with a thickness of 120μm. The coating agent is made by mixing polyurethane resin, hydroxyapatite powder, and di-tert-butyl-p-cresol in a mass ratio of 90:5:5, with a surface pore size of 2-3μm; the particle size is 2-3mm.

[0104] Controlled-release potassium particles: The potassium nutrient core is potassium chloride (potassium content ≥60%), and the carrier is zeolite powder (added at 4% of the mass of potassium chloride); the third polyurethane coating layer is 100μm thick, and the coating agent is made by mixing polyurethane resin, potassium alginate, and di-tert-butyl-p-cresol in a mass ratio of 90:7:3; the particle size is 2-3mm.

[0105] Controlled-release trace element particles: The trace element nutrient core is composed of zinc sulfate, magnesium sulfate, boric acid, and lanthanum nitrate in a mass ratio of 49:30:20:1, and the carrier is diatomaceous earth (added at 8% of the total mass of the trace element raw materials); the citric acid chelation treatment layer is sprayed with a 10% mass concentration citric acid-EDTA disodium mixed solution (mass ratio 8:2), the spraying amount is 5% of the mass of the trace element nutrient core, and the thickness is 15μm; the fourth polyurethane coating layer is 80μm thick, and the coating agent is made by mixing polyurethane resin, humic acid, and di-tert-butyl-p-cresol in a mass ratio of 95:3:2; the particle size is 2-3mm.

[0106] Immediate-release citric acid activated granules: Citric acid mass fraction is 20%, the carrier is a modified composite carrier (diatomaceous earth: bentonite: zeolite powder = 3:2:1, activated at 550℃ for 2.5h, and pulverized to 90 mesh), the amount of carrier added is 2.5 times the mass of citric acid; the particle size is 2-3mm.

[0107] The preparation method is as follows:

[0108] S1. Preparation of controlled-release nitrogen particles: Urea and bentonite were mixed evenly and granulated at 65℃, then dried at 90℃ until the particle moisture content was ≤2%; polyurethane resin, 2-acrylamide-2-methylpropanesulfonic acid, N-isopropylacrylamide, and di-tert-butyl-p-cresol were mixed in a mass ratio of 85:7:5:3, an appropriate amount of acetone was added, and the mixture was reacted at 55℃ for 35 min. After cooling, a modified polyurethane coating agent was obtained; a fluidized bed coating process was used to coat the particles with the coating agent at 50℃, with a coating thickness of 80 μm, to obtain controlled-release nitrogen particles.

[0109] S2. Preparation of controlled-release phosphorus particles: Monoammonium phosphate and diatomaceous earth are mixed evenly and granulated at 70℃, then dried at 95℃ until the particle moisture content is ≤2%; polyurethane resin, hydroxyapatite powder, and di-tert-butyl-p-cresol are mixed at a mass ratio of 90:5:5, and an appropriate amount of sodium bicarbonate is added and stirred evenly to obtain a porous modified polyurethane coating agent; fluidized bed coating process is used to coat the particles with the coating agent at 50℃, and the wind speed is controlled to form 2-3μm air and water permeable pores in the coating layer, with a coating thickness of 120μm, to obtain controlled-release phosphorus particles.

[0110] S3. Preparation of controlled-release potassium element particles: Potassium chloride and zeolite powder are mixed evenly and granulated at 68℃, and then dried at 92℃ until the particle moisture content is ≤2%; polyurethane resin, potassium alginate, and di-tert-butyl-p-cresol are mixed at a mass ratio of 90:7:3, an appropriate amount of acetone is added, and the mixture is stirred evenly to obtain a coating agent; fluidized bed coating process is used to coat the particles with the coating agent at 48℃, and the coating thickness is 100μm to obtain controlled-release potassium element particles.

[0111] S4. Preparation of controlled-release trace element particles: Zinc sulfate, magnesium sulfate, boric acid, lanthanum nitrate, and diatomaceous earth are mixed evenly and granulated at 70℃. The granules are then dried at 95℃ until the moisture content is ≤2%. A 10% (w / w) citric acid-EDTA disodium mixed solution is sprayed (the spraying amount is 5% of the core mass), and dried at 80℃ for 20 min to form a chelation treatment layer with a thickness of 15 μm. Polyurethane resin, humic acid, and di-tert-butyl-p-cresol are mixed at a mass ratio of 95:3:2 and stirred evenly to obtain a coating agent. A fluidized bed coating process is used to coat the particles with this coating agent at 45℃, with a coating thickness of 80 μm, to obtain controlled-release trace element particles.

[0112] S5. Preparation of immediate-release citric acid activated granules: Diatomaceous earth, bentonite, and zeolite powder are mixed in a mass ratio of 3:2:1, placed in a muffle furnace and activated at 550℃ for 2.5h. After cooling, the mixture is pulverized to 90 mesh to obtain a modified composite carrier. Citric acid and the modified composite carrier are mixed evenly in a mass ratio of 1:2.5, granulated at 75℃, and dried at 85℃ until the moisture content of the granules is ≤2% to obtain immediate-release citric acid activated granules.

[0113] S6. Blending: Mix the five types of granules obtained in steps S1-S5 evenly in a mass ratio of 40:20:15:15:10, add 0.2% silica by mass, stir evenly, and then sieve, measure, and package to obtain a multifunctional zoned controlled-release blended fertilizer.

[0114] Technical effects:

[0115] This embodiment modifies and optimizes the coating agent, carrier, and trace element core. The modified polyurethane coating layer (with added 2-acrylamide-2-methylpropanesulfonic acid and N-isopropylacrylamide) improves the flexibility and controlled-release precision of the coating, reducing coating damage. The porous modified phosphorus coating layer (with added hydroxyapatite) can precisely control the phosphorus release rate, adapting to the phosphorus requirements of crops at different growth stages. The controlled-release trace element particles contain lanthanum nitrate, combined with a citric acid-EDTA disodium mixed chelate solution, which significantly improves the stability and absorption rate of trace elements. The modified composite carrier increases the loading capacity and release uniformity of citric acid. The addition of an anti-caking agent effectively prevents fertilizer from clumping during storage and improves fertilizer flowability. This fertilizer improves the controlled release precision of nitrogen, phosphorus, potassium and trace elements by 20%-25%, increases nitrogen utilization by 18%-22%, phosphorus utilization by 16%-20%, potassium utilization by 17%-21%, and increases crop yield by 12%-15%. Moreover, the fertilizer has an agglomeration rate of ≤3% after 6 months of storage, which is far lower than that of ordinary controlled-release fertilizers (agglomeration rate ≥15%).

[0116] Example 5:

[0117] A multifunctional zoned controlled-release blended fertilizer is composed of controlled-release nitrogen granules, controlled-release phosphorus granules, controlled-release potassium granules, controlled-release trace element granules, and controlled-release citric acid activated granules in a mass ratio of 45:15:15:10:15, with an anti-caking agent (silica) of 0.3% by mass added.

[0118] Among them, the controlled-release nitrogen element particles have the following characteristics: the nitrogen element nutrient core is ammonium nitrate (nitrogen content ≥34%), the carrier is zeolite powder (added at 6% of the mass of ammonium nitrate); the first polyurethane coating layer is a modified polyurethane coating layer with a thickness of 70μm, and the coating agent is made by mixing polyurethane resin, 2-acrylamide-2-methylpropanesulfonic acid, N-isopropylacrylamide, and di-tert-butyl-p-cresol in a mass ratio of 88:5:4:3; the particle size is 1-2mm.

[0119] Controlled-release phosphorus particles: The phosphorus nutrient core is diammonium phosphate (phosphorus content ≥48%), and the carrier is bentonite (added at 5% of the mass of diammonium phosphate); the second polyurethane coating layer is a porous modified coating layer with a thickness of 150μm. The coating agent is made by mixing polyurethane resin, hydroxyapatite powder, and di-tert-butyl-p-cresol in a mass ratio of 92:4:4, with a surface pore size of 1-2μm; the particle size is 1-2mm.

[0120] Controlled-release potassium particles: The potassium nutrient core is potassium sulfate (potassium content ≥50%), and the carrier is diatomaceous earth (added at 5% of the mass of potassium sulfate); the third polyurethane coating layer is 120μm thick, and the coating agent is made by mixing polyurethane resin, potassium alginate, and di-tert-butyl-p-cresol in a mass ratio of 91:6:3; the particle size is 1-2mm.

[0121] Controlled-release trace element particles: The trace element nutrient core is composed of copper sulfate, manganese sulfate, boric acid, and cerium nitrate in a mass ratio of 39:40:20:1, and the carrier is bentonite (added at 6% of the total mass of the trace element raw materials); the citric acid chelation treatment layer is sprayed with a 15% mass concentration citric acid-EDTA disodium mixed solution (mass ratio 8:2), the spraying amount is 3% of the mass of the trace element nutrient core, and the thickness is 10μm; the fourth polyurethane coating layer has a thickness of 120μm, and the coating agent is made by mixing polyurethane resin, humic acid, and di-tert-butyl-p-cresol in a mass ratio of 96:2:2; the particle size is 1-2mm.

[0122] Controlled-release citric acid activated granules: Citric acid mass fraction is 30%, the carrier is a modified composite carrier (diatomaceous earth: bentonite: zeolite powder = 3:2:1, activated at 500℃ for 3h, and pulverized to 80 mesh), the amount of carrier added is twice the mass of citric acid; the thickness of the fifth polyurethane coating layer is 50μm; the particle size is 1-2mm.

[0123] The preparation method is as follows:

[0124] S1. Preparation of controlled-release nitrogen particles: Ammonium nitrate and zeolite powder were mixed evenly and granulated at 75℃, then dried at 100℃ until the particle moisture content was ≤2%; polyurethane resin, 2-acrylamido-2-methylpropanesulfonic acid, N-isopropylacrylamide, and di-tert-butyl-p-cresol were mixed in a mass ratio of 88:5:4:3, and an appropriate amount of acetone was added. The mixture was reacted at 50℃ for 40 min, and after cooling, a modified polyurethane coating agent was obtained; a fluidized bed coating process was used to coat the particles with the coating agent at 60℃, and the coating thickness was 70 μm, thus obtaining controlled-release nitrogen particles.

[0125] S2. Preparation of controlled-release phosphorus particles: Diammonium phosphate and bentonite are mixed evenly and granulated at 72℃, then dried at 98℃ until the particle moisture content is ≤2%; polyurethane resin, hydroxyapatite powder, and di-tert-butyl-p-cresol are mixed at a mass ratio of 92:4:4, and an appropriate amount of sodium bicarbonate is added and stirred evenly to obtain a porous modified polyurethane coating agent; fluidized bed coating process is used to coat the particles with the coating agent at 55℃, and the wind speed is controlled to form 1-2μm air and water permeable pores in the coating layer, with a coating thickness of 150μm, to obtain controlled-release phosphorus particles.

[0126] S3. Preparation of controlled-release potassium particles: Potassium sulfate and diatomaceous earth are mixed evenly and granulated at 70℃, then dried at 96℃ until the particle moisture content is ≤2%; polyurethane resin, potassium alginate, and di-tert-butyl-p-cresol are mixed at a mass ratio of 91:6:3, an appropriate amount of acetone is added, and the mixture is stirred evenly to obtain a coating agent; fluidized bed coating process is used to coat the particles with the coating agent at 52℃, and the coating thickness is 120μm to obtain controlled-release potassium particles.

[0127] S4. Preparation of controlled-release trace element particles: Copper sulfate, manganese sulfate, boric acid, cerium nitrate, and bentonite are mixed evenly and granulated at 80℃. The granules are then dried at 100℃ until the moisture content is ≤2%. A 15% (w / w) citric acid-EDTA disodium mixed solution is sprayed (the spraying amount is 3% of the core mass), and dried at 90℃ for 15 min to form a chelation treatment layer with a thickness of 10 μm. Polyurethane resin, humic acid, and di-tert-butyl-p-cresol are mixed at a mass ratio of 96:2:2 and stirred evenly to obtain a coating agent. A fluidized bed coating process is used to coat the particles with this coating agent at 55℃, resulting in a coating thickness of 120 μm, thus obtaining controlled-release trace element particles.

[0128] S5. Preparation of controlled-release citric acid activated granules: Diatomaceous earth, bentonite, and zeolite powder are mixed in a mass ratio of 3:2:1, and activated at 500℃ for 3 hours in a muffle furnace. After cooling, the mixture is pulverized to 80 mesh to obtain a modified composite carrier. Citric acid and the modified composite carrier are mixed evenly in a mass ratio of 1:2, granulated at 80℃, and dried at 90℃ until the particle moisture content is ≤2%. A fluidized bed coating process is used to coat the particles with a polyurethane coating agent at 40℃, with a coating thickness of 50μm, to obtain controlled-release citric acid activated granules.

[0129] S6. Blending: Mix the five types of granules obtained in steps S1-S5 evenly in a mass ratio of 45:15:15:10:15, add 0.3% silica by mass, stir evenly, and then sieve, measure, and package to obtain a multifunctional zoned controlled-release blended fertilizer.

[0130] Technical effects:

[0131] This embodiment optimizes the ratio of the modified coating agent, improving the density and stability of the coating. Simultaneously, it adjusts the pore size of the porous coating layer (1-2 μm) to further precisely control phosphorus release. The controlled-release micronutrient granules, with the addition of cerium nitrate, synergistically enhance the chelation effect and crop absorption efficiency of micronutrients with disodium citric acid-EDTA. Controlled-release citric acid activating granules, combined with a modified composite carrier, achieve slow and continuous release of citric acid, extending soil activation time. The amount of anti-caking agent added is optimized to further reduce fertilizer caking rate. The controlled-release period for nitrogen is 60-70 days, for phosphorus 100-110 days, for potassium 90-100 days, and for micronutrients 80-90 days. When applied to fruit and vegetable cultivation, it increases yield by 13%-16%, vitamin content by 6.5%-8.2%, reduces fruit deformity rate by 4.8%-5.5%, and the caking rate is ≤2% after 6 months of storage. Its overall performance is superior to that of Examples 1-4.

[0132] Example 6:

[0133] A multifunctional zoned controlled-release blended fertilizer is composed of controlled-release nitrogen granules, controlled-release phosphorus granules, controlled-release potassium granules, controlled-release trace element granules, and fast-release citric acid activated granules in a mass ratio of 30:25:20:20:5, with an anti-caking agent (silica) of 0.1% by mass added.

[0134] Among them, the controlled-release nitrogen element particles have the following characteristics: the nitrogen element nutrient core is ammonium chloride (nitrogen content ≥25%), the carrier is diatomaceous earth (added at 4% of the mass of ammonium chloride); the first polyurethane coating layer is a modified polyurethane coating layer with a thickness of 100μm, and the coating agent is made by mixing polyurethane resin, 2-acrylamide-2-methylpropanesulfonic acid, N-isopropylacrylamide, and di-tert-butyl-p-cresol in a mass ratio of 82:10:5:3; the particle size is 3-4mm.

[0135] Controlled-release phosphorus particles: The phosphorus nutrient core is monoammonium phosphate (phosphorus content ≥46%), and the carrier is zeolite powder (added at 7% of the mass of monoammonium phosphate); the second polyurethane coating layer is a porous modified coating layer with a thickness of 110μm. The coating agent is made by mixing polyurethane resin, hydroxyapatite powder, and di-tert-butyl-p-cresol in a mass ratio of 89:5:6, with a surface pore size of 3-5μm and a particle size of 3-4mm.

[0136] Controlled-release potassium granules: The potassium nutrient core is potassium chloride (potassium content ≥60%), and the carrier is bentonite (added at 6% of the mass of potassium chloride); the third polyurethane coating layer is 90μm thick, and the coating agent is made by mixing polyurethane resin, potassium alginate, and di-tert-butyl-p-cresol in a mass ratio of 89:8:3; the particle size is 3-4mm.

[0137] Controlled-release trace element particles: The trace element nutrient core is composed of zinc sulfate, manganese sulfate, magnesium sulfate, and lanthanum nitrate in a mass ratio of 29:30:40:1, and the carrier is zeolite powder (added at 10% of the total mass of the trace element raw materials); the citric acid chelation treatment layer is sprayed with a 5% mass concentration citric acid-EDTA disodium mixed solution (mass ratio 8:2), the spraying amount is 8% of the mass of the trace element nutrient core, and the thickness is 20μm; the fourth polyurethane coating layer is 100μm thick, and the coating agent is made by mixing polyurethane resin, humic acid, and di-tert-butyl-p-cresol in a mass ratio of 93:4:3; the particle size is 3-4mm.

[0138] Immediate-release citric acid activated granules: Citric acid mass fraction is 10%, the carrier is a modified composite carrier (diatomaceous earth: bentonite: zeolite powder = 3:2:1, activated at 600℃ for 2h, and pulverized to 100 mesh), the amount of carrier added is 3 times the mass of citric acid; the particle size is 3-4mm.

[0139] The preparation method is as follows:

[0140] S1. Preparation of controlled-release nitrogen particles: Ammonium chloride and diatomaceous earth are mixed evenly and granulated at 60℃, then dried at 80℃ until the particle moisture content is ≤2%; polyurethane resin, 2-acrylamide-2-methylpropanesulfonic acid, N-isopropylacrylamide, and di-tert-butyl-p-cresol are mixed in a mass ratio of 82:10:5:3, an appropriate amount of acetone is added, and the mixture is reacted at 60℃ for 30 min. After cooling, a modified polyurethane coating agent is obtained; using a fluidized bed coating process, the coating agent is used to coat the particles at 40℃, with a coating thickness of 100 μm, to obtain controlled-release nitrogen particles.

[0141] S2. Preparation of controlled-release phosphorus particles: Monoammonium phosphate and zeolite powder are mixed evenly and granulated at 65℃, then dried at 88℃ until the particle moisture content is ≤2%; polyurethane resin, hydroxyapatite powder, and di-tert-butyl-p-cresol are mixed at a mass ratio of 89:5:6, and an appropriate amount of sodium bicarbonate is added and stirred evenly to obtain a porous modified polyurethane coating agent; fluidized bed coating process is used to coat the particles with the coating agent at 45℃, and the wind speed is controlled to form 3-5μm air and water permeable pores in the coating layer, with a coating thickness of 110μm, to obtain controlled-release phosphorus particles.

[0142] S3. Preparation of controlled-release potassium particles: Potassium chloride and bentonite are mixed evenly and granulated at 62℃, and then dried at 85℃ until the particle moisture content is ≤2%; polyurethane resin, potassium alginate, and di-tert-butyl-p-cresol are mixed at a mass ratio of 89:8:3, an appropriate amount of acetone is added, and the mixture is stirred evenly to obtain a coating agent; fluidized bed coating process is used to coat the particles with the coating agent at 42℃, and the coating thickness is 90μm to obtain controlled-release potassium particles.

[0143] S4. Preparation of controlled-release trace element particles: Zinc sulfate, manganese sulfate, magnesium sulfate, lanthanum nitrate, and zeolite powder are mixed evenly and granulated at 65℃. The granules are then dried at 85℃ until the moisture content is ≤2%. A 5% (w / w) citric acid-EDTA disodium mixed solution is sprayed (the spraying amount is 8% of the core mass), and dried at 70℃ for 30 min to form a chelation treatment layer with a thickness of 20 μm. Polyurethane resin, humic acid, and di-tert-butyl-p-cresol are mixed at a mass ratio of 93:4:3 and stirred evenly to obtain a coating agent. A fluidized bed coating process is used to coat the particles with this coating agent at 50℃, with a coating thickness of 100 μm, to obtain controlled-release trace element particles.

[0144] S5. Preparation of immediate-release citric acid activated granules: Diatomaceous earth, bentonite, and zeolite powder are mixed in a mass ratio of 3:2:1, and activated at 600℃ for 2 hours in a muffle furnace. After cooling, the mixture is pulverized to 100 mesh to obtain a modified composite carrier. Citric acid and the modified composite carrier are mixed evenly in a mass ratio of 1:3, granulated at 65℃, and dried at 80℃ until the moisture content of the granules is ≤2% to obtain immediate-release citric acid activated granules.

[0145] S6. Blending: Mix the five types of granules obtained in steps S1-S5 evenly in a mass ratio of 30:25:20:20:5, add 0.1% by mass of silica, stir evenly, and then sieve, measure, and package to obtain a multifunctional zoned controlled-release blended fertilizer.

[0146] Technical effects:

[0147] This embodiment optimizes the formulation ratio of each particle to meet the needs of crops in saline-alkali land. The ammonium chloride core is combined with a high proportion of modified coating agent to further improve the stability of nitrogen and reduce the harm of chloride ions. The porous phosphorus coating layer has an increased pore size (3-5μm) to accelerate the initial release of phosphorus and meet the phosphorus requirements of crops in the seedling stage in saline-alkali land. The chelation treatment layer of the controlled-release trace element particles is thickened (20μm) to improve the chelation stability of trace elements and reduce soil fixation. The modified composite carrier is activated at 600℃ to improve the adsorption performance and citric acid loading of the carrier. This fertilizer is suitable for complex environments such as saline-alkali land and barren soil. The controlled release period of nitrogen can reach 75-85 days, phosphorus can reach 90-100 days, potassium can reach 80-90 days, and micronutrients can reach 85-95 days. When applied to wheat planting in saline-alkali land, wheat yield increases by 10%-13%, stress resistance (drought resistance and salt tolerance) is significantly enhanced, soil organic matter content increases by 5.0%-5.8%, and soil pH decreases by 0.3-0.5 units, showing outstanding soil improvement effect.

[0148] Comparative Example 1 (without zoned controlled release, no citric acid activated particles):

[0149] A blended fertilizer is made by mixing urea, monoammonium phosphate, potassium chloride, zinc sulfate, magnesium sulfate, and boric acid in a mass ratio of 40:20:15:7.5:4.5:3. It has no coating treatment and no citric acid activated particles. The other parameters are the same as those in Example 1.

[0150] Technical effects: This fertilizer has no controlled-release function, and the nutrient release rate is fast. The nitrogen volatilization loss rate is 35%-40%, the phosphorus fixation rate is 45%-50%, and the micronutrient utilization rate is ≤30%. Crops are prone to nutrient deficiency in the later stages of growth, and wheat yield is only increased by 1.2%-2.5%. Soil compaction problem is not improved, and the fertilizer is prone to clumping. The clumping rate is ≥25% after 3 months of storage.

[0151] Comparative Example 2 (using a single coating, without citric acid chelation treatment):

[0152] A controlled-release blended fertilizer is composed of controlled-release nitrogen granules, controlled-release phosphorus granules, controlled-release potassium granules, ordinary trace element granules, and fast-release citric acid activated granules in a mass ratio of 40:20:15:15:10. Each controlled-release granule is coated with ordinary polyurethane (unmodified), and the trace element granules are not treated with citric acid chelation. The remaining parameters are consistent with those in Example 1.

[0153] Technical effects: This fertilizer has low controlled-release precision, the coating is easily damaged, the controlled-release period of nitrogen is only 30-40 days, the controlled-release period of phosphorus is 40-50 days, and the controlled-release period of potassium is 35-45 days; micronutrients are not chelated and are easily fixed by the soil, with a utilization rate of only 35%-40%; wheat yield is increased by 4.8%-6.2%, and nutrient utilization rate is increased by 6%-8%, but the overall effect is far lower than that of Examples 1-6.

[0154] Comparative Example 3 (unmodified coating and modified carrier):

[0155] A controlled-release blended fertilizer has the same formula and preparation process as in Example 4, but each controlled-release particle is coated with ordinary polyurethane (without modification), and the fast-release citric acid activated particles are carried by ordinary zeolite powder (without high-temperature activation), and no anti-caking agent is added.

[0156] Technical effects: The fertilizer coating has poor flexibility, and the coating damage rate is ≥15% during storage, resulting in decreased controlled release accuracy. Nitrogen utilization rate only increases by 10%-12%, and phosphorus utilization rate increases by 8%-10%. The citric acid release of the citric acid activated granules is uneven, resulting in limited soil activation effect. After 6 months of fertilizer storage, the clumping rate is ≥18%, and the crop yield increases by 7.5%-9.0%. The overall performance is significantly lower than that of Example 4.

[0157] Comparative Example 4 (Citrate-activated particles were ordinary particles, without controlled-release / immediate-release optimization)

[0158] A controlled-release blended fertilizer has the same formula and preparation process as in Example 5, but the controlled-release citric acid activated granules are replaced with ordinary citric acid granules (without coating or modified carrier), while the other parameters remain unchanged.

[0159] Technical effects: Citric acid is rapidly lost, the soil activation cycle is short (only 7-10 days), and it cannot continuously promote nutrient activation; the utilization rate of phosphorus, potassium and trace elements is only increased by 10%-12%; the yield of fruits and vegetables is increased by 5.8%-7.2%, the improvement in fruit quality is not obvious, and the overall effect is lower than that of Example 5.

[0160] In summary, Examples 1-6 of this invention, through the synergistic design of "regional controlled release + citric acid activation + modification optimization," demonstrate significant inventiveness compared to Comparative Examples 1-4, specifically manifested in the following ways:

[0161] 1. Zoned controlled release design: Nitrogen, phosphorus, potassium, and trace elements are made into independent controlled release granules. Based on the crop requirements for each nutrient, different thicknesses and types of coating layers are designed to achieve precise controlled release of each nutrient, solving the problems of asynchronous nutrient release and low utilization rate in traditional blended fertilizers.

[0162] 2. Citric acid activation synergy: The combination of fast-release / controlled-release citric acid activation particles and citric acid chelation treatment can not only adjust the soil pH and activate fixed nutrients in the soil, but also improve the stability and absorption rate of trace elements, thus solving the technical pain points of soil nutrient fixation and low utilization rate of trace elements.

[0163] 3. Modified and optimized design: By modifying the coating agent (to improve the controlled release accuracy and coating stability), modifying the composite carrier (to improve adsorption and loading capacity), and adding rare earth elements (lanthanum nitrate, cerium nitrate), the controlled release performance, nutrient utilization rate and anti-caking ability of the fertilizer are further improved, making it suitable for different soil environments (ordinary soil, saline-alkali land) and crop needs.

[0164] 4. Excellent overall effect: Compared with the comparative example, the fertilizer nutrient utilization rate of the embodiment of the present invention is increased by 12%-22%, the crop yield is increased by 7.8%-16%, the soil improvement effect is significant, and the fertilizer has good storage stability and low caking rate. It solves the technical problems of poor control release precision, nutrient waste and weak soil adaptability of traditional controlled release fertilizers, and has outstanding technical advantages and creativity.

[0165] 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; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multifunctional zoned controlled-release blended fertilizer, characterized in that, Functional particles, formed by physical blending of one or more of the following methods, wherein each functional particle is independently coated to achieve synergistic controlled release of multiple elements, include: Controlled-release nitrogen particles: comprising a nitrogen nutrient core and a first polyurethane coating layer covering the surface of the nitrogen nutrient core, wherein the nitrogen nutrient core is made from at least one of urea, ammonium chloride, and ammonium nitrate; Controlled-release phosphorus particles: comprising a phosphorus nutrient core and a second polyurethane coating layer covering the surface of the phosphorus nutrient core, wherein the phosphorus nutrient core is made from at least one of monoammonium phosphate and diammonium phosphate; Controlled-release potassium particles: comprising a potassium nutrient core and a third polyurethane coating layer covering the surface of the potassium nutrient core, wherein the potassium nutrient core is made from at least one of potassium chloride and potassium sulfate; Controlled-release trace element particles: comprising a trace element nutrient core and a fourth polyurethane coating layer covering the surface of the trace element nutrient core, wherein the trace element nutrient core contains at least one trace element; Citric acid activated particles: comprising citric acid and a carrier, wherein the citric acid activated particles are of the immediate-release type or the controlled-release type, and the surface of the controlled-release citric acid activated particles is coated with a fifth polyurethane coating layer.

2. The multifunctional zoned controlled-release blended fertilizer according to claim 1, characterized in that, The surface of the trace element nutrient core of the controlled-release trace element particles is also provided with a citric acid chelation treatment layer, which is formed by spraying a citric acid solution onto the dried trace element nutrient core.

3. The multifunctional zoned controlled-release blended fertilizer according to claim 1, characterized in that, The controlled-release nitrogen particles, controlled-release phosphorus particles, and controlled-release potassium particles do not contain citric acid in their nutrient cores; they achieve independent controlled release only through their respective corresponding polyurethane coating layers.

4. The multifunctional zoned controlled-release blended fertilizer according to claim 1, characterized in that, The trace elements are selected from at least one of zinc, magnesium, copper, manganese, and boron.

5. The multifunctional zoned controlled-release blended fertilizer according to claim 1, characterized in that, The citric acid activated particles contain 10%-30% citric acid by mass, and the carrier is at least one of diatomaceous earth, bentonite, and zeolite powder.

6. The multifunctional zoned controlled-release blended fertilizer according to claim 1, characterized in that, The controlled-release nitrogen particles, controlled-release phosphorus particles, controlled-release potassium particles, controlled-release trace element particles, and citric acid activated particles all have a particle size of 1-4 mm; the thickness of the first, second, third, fourth, and fifth polyurethane coating layers is 50-200 μm.

7. The multifunctional zoned controlled-release blended fertilizer according to claim 1, characterized in that, The mass ratio of the controlled-release nitrogen particles, controlled-release phosphorus particles, controlled-release potassium particles, controlled-release trace element particles, and citric acid activated particles is as follows: (30-45):(15-25):(10-20):(10-20):(5-15)。 8. A method for preparing the multifunctional zoned controlled-release blended fertilizer according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Preparation of controlled-release nitrogen element particles: Nitrogen element raw materials are mixed evenly with a carrier, granulated and dried, and then coated with a polyurethane coating agent to obtain controlled-release nitrogen element particles. S2. Preparation of controlled-release phosphorus particles: The phosphorus raw material is mixed evenly with the carrier, granulated and dried, and then coated with a polyurethane coating agent to obtain controlled-release phosphorus particles. S3. Preparation of controlled-release potassium element particles: The potassium element raw material is mixed evenly with the carrier, granulated and dried, and then coated with a polyurethane coating agent to obtain controlled-release potassium element particles. S4. Preparation of controlled-release trace element particles: The trace element raw materials are mixed evenly with the carrier, granulated and dried, and then sprayed with citric acid solution for surface chelation treatment. After drying again, polyurethane coating agent is used for coating treatment to obtain controlled-release trace element particles. S5. Preparation of citric acid activated granules: Citric acid and carrier are mixed evenly, granulated and dried to obtain immediate-release citric acid activated granules; or granulated and dried, and then coated with a polyurethane coating agent to obtain controlled-release citric acid activated granules. S6. Blending: Mix the five functional granules obtained in steps S1 to S5 evenly according to a preset mass ratio to obtain a multifunctional zoned controlled-release blended fertilizer.

9. The preparation method according to claim 8, characterized in that, In steps S1 to S5, the granulation temperature is 60-80℃, the drying temperature is 80-100℃, and the granules are dried until the moisture content is ≤2%; the coating treatment adopts a fluidized bed coating process, and the coating temperature is 40-60℃.

10. The preparation method according to claim 8, characterized in that, In step S4, the mass concentration of the citric acid solution is 5%-15%, and the spraying amount is 3%-8% of the mass of the trace element nutrient core; the drying temperature after spraying is 70-90℃, and the drying time is 15-30min.

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