A slow-release fertilizer and a preparation method and application thereof

Abstract

This invention relates to a controlled-release fertilizer, its preparation method, and its application. The controlled-release fertilizer comprises a fertilizer core material and a base coating, an inner control layer, and an outer control layer sequentially coated on the surface of the fertilizer core material. The base coating comprises a bio-based polyol; the inner control layer comprises polyurethane; and the outer control layer comprises polyvinyl alcohol and bentonite. The bentonite comprises bentonite calcined at 800-1000℃. The total thickness of the base coating, inner control layer, and outer control layer is 200-300 μm. The controlled-release fertilizer provided by this invention exhibits excellent mechanical stability, a long nutrient release period, and is suitable for the nutrient requirements of rice during its growth cycle, effectively preventing seedling burn and nutrient deficiency during the heading, flowering, and grain-filling stages.

Description

Technical Field

[0001] This invention relates to the field of agricultural fertilizer technology, and in particular to a slow-release fertilizer, its preparation method, and its application. Background Technology

[0002] From day 1 to 10 after rice transplanting, the rice seedlings are small and grow slowly, requiring relatively little nutrition. From day 11 to 30, the rice is in the tillering stage, a period of vigorous growth where nutrient demand increases. From day 31 to 60, the rice is in the jointing stage, a period of simultaneous vegetative and reproductive growth, requiring stable nutrients to promote panicle differentiation and development. From day 61 to 90, the rice is in the heading and flowering stage, where nutrient demand increases again. From day 90 to 110, the rice is in the grain-filling stage, where nutrient deficiency must be avoided to improve the grain filling rate and grain weight.

[0003] With the popularization of dry-seedling technology, the quality of rice seedlings has an increasingly significant impact on the rate of seedling recovery after transplanting. Rice transplanting fertilizer is a key fertilizer connecting the rice seedling stage and field growth, and it needs to take into account the dual goals of promoting root growth and strong seedlings as well as controlled release and long-lasting effect. Existing slow-release fertilizers have the defects of single release rate, are greatly affected by temperature and humidity, and the release mode is mostly linear slow release, with a fast release rate in the early stage and a slow release rate in the later stage. The nutrient release period is short and it is difficult to adapt to the nutrient requirements of rice growth cycle. It is easy to cause problems such as seedling burn in the seedling stage, nutrient deficiency in the heading, flowering and grain filling stages, and low nutrient utilization rate. In addition, the coating materials used in traditional slow-release fertilizers have problems such as difficulty in molding, low mechanical strength, insufficient environmental protection, and difficulty in degradation of some components. Even slow-release fertilizers with multi-layer coatings have poor interfacial compatibility between coating layers, which are prone to peeling or damage, resulting in uncontrolled nutrient release. This leads to rapid or incomplete release of nutrients, leaving residues in the soil, affecting soil fertility, and low fertilizer utilization rate.

[0004] Therefore, it is necessary to develop a slow-release fertilizer with a long nutrient release period that can adapt to the nutrient requirements of rice during its growth cycle. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a controlled-release fertilizer, its preparation method, and its application. The controlled-release fertilizer exhibits excellent mechanical stability, is compatible with the nutrient requirements of rice during its growth cycle, and has a long nutrient release period, effectively preventing seedling burn during the seedling stage and nutrient deficiency during the heading, flowering, and grain-filling stages.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a controlled-release fertilizer, the controlled-release fertilizer comprising a fertilizer core material and a base coating, an inner control layer, and an outer control layer sequentially coated on the surface of the fertilizer core material; the base coating comprises a bio-based polyol; the inner control layer comprises polyurethane; the outer control layer comprises polyvinyl alcohol and bentonite; the bentonite comprises bentonite calcined at 800~1000℃ (e.g., 820℃, 840℃, 860℃, 880℃, 900℃, 920℃, 940℃, 960℃, or 980℃, etc.); the total thickness of the base coating, inner control layer, and outer control layer is 200~300 μm, for example 210 μm, 220 μm, 230 μm, 240 μm, 250 μm, 260 μm, 270 μm, 280 μm, or 290 μm, etc.

[0007] Preferably, the total thickness of the base layer, inner control layer and outer control layer is 240~300 μm.

[0008] In this invention, the fertilizer core material provides basic nutrients for rice from the seedling stage to the grain-filling stage; the bio-based polyol in the base layer has good biocompatibility and initial barrier properties, which can initially delay nutrient release; the inner control layer, made of polyurethane, can further extend the nutrient diffusion path and enhance the controlled-release effect; the outer control layer, composed of polyvinyl alcohol and bentonite, forms an aggregated textured structure with porous and low connectivity, which can further inhibit nutrient release and extend the release period, and the total thickness of the base layer, inner control layer, and outer control layer is controlled at 200-300 mm. The micrometer-wide coating allows the three layers of the slow-release fertilizer—the base layer, the inner control layer, and the outer control layer—to work synergistically, precisely covering all the key nutrient-demanding stages of rice from the seedling stage to the grain-filling stage. During the seedling stage (approximately days 1-10 after transplanting), the nutrient release rate of the slow-release fertilizer is low, effectively preventing seedling burn. During the tillering stage (approximately days 11-30), which is the first peak period for rice nutrient demand, the nutrient release rate of the slow-release fertilizer also increases, reaching its first peak. During the jointing stage (approximately days 31-60), rice requires stable nutrients, and the nutrient release rate of the slow-release fertilizer is stable during this period. From days 61-90... During the heading and flowering stage, rice's nutrient demand increases again. The nutrient release rate of the controlled-release fertilizer increases again during this period, reaching a second peak on day 90. From day 90 to 110, approximately during the grain-filling stage, the nutrient release rate of the controlled-release fertilizer increases slightly, preventing nutrient deficiency. The nutrient release rhythm matches the stage-specific nutrient requirements of rice, avoiding seedling burn caused by concentrated nutrient release in the early stages and mitigating the risk of nutrient deficiency due to insufficient nutrient supply in the later stages. With its long nutrient release period, the controlled-release fertilizer solves the problem that the traditional linear controlled-release fertilizer model cannot meet the dynamic nutrient requirements of rice during growth.

[0009] In this invention, bentonite is calcined at 800-1000℃, which improves the stability of its pore structure and its adsorption performance. The outer control layer formed by combining calcined bentonite with polyvinyl alcohol has reduced connectivity in its porous structure, allowing the controlled-release fertilizer to release nutrients stably during the rice jointing stage. Subsequent nutrient release periods will see a second peak, matching the varying nutrient requirements of rice at different stages. Furthermore, the outer control layer's resistance to water erosion is enhanced, resulting in a low breakage rate of the controlled-release fertilizer after field application, ensuring the stability of the controlled-release effect throughout the entire process. If bentonite is not calcined or the calcination temperature is too low, the interlayer water and organic impurities inside the bentonite cannot be fully removed, resulting in insufficient stability of the pore structure. When bentonite is mixed with polyvinyl alcohol to prepare an external control coating solution, it is prone to sedimentation, causing the external control coating solution to separate into layers and resulting in uneven dispersion. At the same time, it is easy to clog the nozzle during spraying. If the temperature is higher than 1000℃, the crystal structure of bentonite will be irreversibly destroyed, the pores of bentonite will collapse, its ability to adsorb and impound nutrients will be greatly reduced, the nutrient control release performance will be weakened, and the nutrient release period will be shortened. In this invention, the total thickness of the base layer, inner control layer, and outer control layer is 200-300 μm. If the total thickness of the base layer, inner control layer, and outer control layer is less than 200 μm, the blocking ability is insufficient, the nutrient release period is too short, and the rice is prone to nutrient deficiency in the later stages of growth, and may even fail to cover the full nutrient requirement stages from the seedling stage to the grain-filling stage. If the total thickness of the base layer, inner control layer, and outer control layer is greater than 300 μm, the nutrient diffusion resistance is too large, the nutrient release period is too long, the nutrient release rate is too low in the early stage of rice jointing, the nutrient release amount is low in the tillering stage and rice jointing stage, and the rice shows symptoms of nutrient deficiency after the jointing stage, which does not match the demand cycle of rice growth and development.

[0010] Preferably, the fertilizer core material comprises the following components: nitrogen fertilizer, phosphorus-potassium compound fertilizer, potassium fertilizer, and silicon-calcium-magnesium fertilizer.

[0011] Preferably, the total nutrient content of the fertilizer core material is ≥45%, such as 50%, 55%, 60%, 65% or 70%.

[0012] It should be noted that regarding the content of nitrogen, phosphorus, and potassium nutrients in the fertilizer, the nitrogen content is expressed as a mass percentage of nitrogen; the phosphorus content is expressed as a mass percentage of P2O5; and the potassium content is expressed as a mass percentage of K2O. Similarly, in this invention, P is expressed as a mass percentage of P2O5, and K is expressed as a mass percentage of K2O. The total nutrient content refers to the total content of N, P2O5, and K2O in the fertilizer core material.

[0013] In this invention, the total nutrient content of the fertilizer core material is ≥45%, and combined with the auxiliary filling of silicon-calcium-magnesium fertilizer, it provides the secondary and trace elements required by rice. This ensures the sufficiency of basic nutrients while avoiding the problems of excessive hygroscopicity and nutrient monotony associated with single high-concentration fertilizer core materials. Simultaneously, this nutrient concentration is suitable for the slow-release mode formed by the base layer, inner control layer, and outer control layer, preventing the risk of concentrated release due to excessively rapid initial nutrient release. By controlling the total nutrient content of the fertilizer core material to preferably ≥45%, sufficient nitrogen, phosphorus, and potassium basic nutrient reserves are provided for rice from the seedling stage to the grain-filling stage, and the nutrient supply to rice at each growth stage remains within the required threshold. This avoids the need for additional fertilizer application due to insufficient nutrients, reduces field management costs, and helps increase the number of tillers and root vitality of rice seedlings, thereby increasing rice yield.

[0014] Preferably, the nitrogen fertilizer includes urea.

[0015] Preferably, the phosphorus-potassium compound fertilizer includes potassium dihydrogen phosphate.

[0016] Preferably, the potassium fertilizer includes potassium chloride.

[0017] Preferably, the fertilizer core material further includes a water-soluble binder.

[0018] Preferably, the water-soluble binder comprises sodium carboxymethyl cellulose.

[0019] Preferably, the water-soluble binder in the fertilizer core material has a mass percentage of 0.2% to 0.3%, such as 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, or 0.29%.

[0020] In this invention, the water-soluble binder is water-soluble and gradually dissolves upon contact with water during subsequent application, without long-term inhibition of the basic release of nutrients from the fertilizer core material, thus adapting to the low fertilizer requirement rhythm in the early stage of rice seedlings. Adding the water-soluble binder to the fertilizer core material enhances the adhesion between nitrogen fertilizer, phosphorus-potassium compound fertilizer, potassium fertilizer, and silicon-calcium-magnesium fertilizer, aiding in the formation of spherical fertilizer core materials during granulation, while ensuring particle uniformity and structural stability, and improving the pelleting rate. The preferred mass percentage of the water-soluble binder in the fertilizer core material is 0.2%~0.3%. By precisely controlling the amount of water-soluble binder added during granulation, a higher pelleting rate and better structural stability of the fertilizer core material can be achieved, resulting in a low breakage rate during transport after granulation. It also provides a regular base for the uniform adhesion of the subsequent base coating, inner control layer, and outer control layer, avoiding uneven coating thickness caused by irregular fertilizer core material morphology, and contributing to the stable achievement of subsequent controlled-release performance standards. If the mass percentage is less than 0.2%, the bonding force between the raw materials of the fertilizer core material is insufficient, the fertilizer core material is easy to loosen, the pelleting rate is low, and the mechanical stability is poor. If the mass percentage is higher than 0.3%, the fertilizer core material will be too hard due to excessive bonding, which will not only increase the energy consumption and pelleting rate of granulation, but also reduce the adhesion between the coating layer composed of the subsequent base coating, inner control layer and outer control layer and the fertilizer core material.

[0021] Preferably, the fertilizer core material is spherical in shape.

[0022] Preferably, the fertilizer core material comprises the following components by weight: 40-45 parts nitrogen fertilizer (e.g., 40.5 parts, 41.0 parts, 41.5 parts, 42.0 parts, 42.5 parts, 43.0 parts, 43.5 parts, 44.0 parts, or 44.5 parts, etc.), and 20-25 parts phosphorus and potassium compound fertilizer (e.g., 20.5 parts, 21.0 parts, 21.5 parts, 22.0 parts, 22.5 parts, 23.0 parts, 23.5 parts, etc.). 4.0 parts or 24.5 parts, etc.), 10-15 parts of potassium fertilizer (e.g., 10.5 parts, 11.0 parts, 11.5 parts, 12.0 parts, 12.5 parts, 13.0 parts, 13.5 parts, 14.0 parts or 14.5 parts, etc.), and 10-15 parts of silicon-calcium-magnesium fertilizer (e.g., 10.5 parts, 11.0 parts, 11.5 parts, 12.0 parts, 12.5 parts, 13.0 parts, 13.5 parts, 14.0 parts or 14.5 parts, etc.).

[0023] Preferably, the average thickness of the base coating is 50~80 μm, such as 55 μm, 60 μm, 65 μm, 70 μm or 75 μm.

[0024] Preferably, the average thickness of the inner control layer is 80~120 μm, such as 85 μm, 90 μm, 95 μm, 100 μm, 105 μm, 110 μm or 115 μm.

[0025] Preferably, the average thickness of the outer control layer is 60~100 μm, such as 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm or 95 μm.

[0026] Preferably, the base coating further includes an emulsifier.

[0027] Preferably, the mass of the emulsifier is 0.125% to 0.25% of the mass of the bio-based polyol, such as 0.14%, 0.16%, 0.18%, 0.20%, 0.22%, or 0.24%.

[0028] In this invention, the combination of bio-based polyol and emulsifier can improve the dispersion uniformity of the base coating liquid and avoid the problem of uneven thickness of the base coating caused by droplet aggregation during coating.

[0029] Preferably, the emulsifier comprises Tween-80.

[0030] Preferably, the bio-based polyols include soybean oil-based polyols and / or castor oil-based polyols.

[0031] In this invention, the bio-based polyol preferably includes soybean oil-based polyol and / or castor oil-based polyol. Soybean oil-based polyol has the advantages of wide availability of raw materials and relatively low cost, while castor oil-based polyol has a higher content of hydroxyl functional groups, resulting in better flexibility and mechanical wear resistance after film formation. When the two are mixed in any proportion, the hydroxyl groups can fully synergize with the emulsifier without phase separation problems, thus balancing the preparation cost and the basic performance of the base coating, and adapting to the needs of different production scenarios.

[0032] In this invention, by selecting soybean oil-based polyols and / or castor oil-based polyols as the core raw materials for the base coating, it can reduce the dependence on petrochemical coating materials by relying on their bio-based properties (bio-based content can reach ≥70%), and also achieve good adhesion between the base coating and the fertilizer core material by leveraging their good interfacial compatibility. At the same time, it can control the nutrient release of the slow-release fertilizer at a low level during the rice seedling stage, precisely matching the low fertilizer requirement rhythm of the rice seedling stage.

[0033] Preferably, the raw materials for preparing the polyurethane include isocyanate, polyether polyol and crosslinking agent.

[0034] In this invention, the inner control layer is preferably formed by the reaction of isocyanate, polyether polyol and crosslinking agent to form a dense polyurethane crosslinked network structure, which helps to extend the nutrient diffusion path.

[0035] In this invention, the controlled-release fertilizer exhibits good mechanical stability and high pressure strength. The dense polyurethane cross-linked structure of the inner control layer provides core support, which, combined with the flexible membrane layers of the base layer and outer control layer, synergistically enhances the fertilizer. This ensures mechanical stability without compromising dispersibility during subsequent field application due to excessive hardness, allowing nutrients to be released in the desired manner. This helps reduce the coefficient of variation in rice seedling height, improves uniform growth, and minimizes nutrient waste caused by particle breakage. Furthermore, it helps adapt to the requirements of practical application scenarios, resulting in a low breakage rate during storage and transportation, thus preventing coating layer failure due to particle breakage and enabling rapid, large-scale nutrient release in a short period.

[0036] Preferably, the molar ratio of the isocyanate to the polyether polyol is (0.9~1.5):1, for example, 1.0:1, 1.1:1, 1.2:1, 1.3:1 or 1.4:1, etc.

[0037] In this invention, the preferred molar ratio of isocyanate to polyether polyol is (0.9~1.5):1, which ensures sufficient cross-linking reaction between the two to form a dense polyurethane film. The added cross-linking agent further increases the cross-linking density of the polyurethane film, enhances its mechanical toughness, and reduces the risk of damage to the inner control layer during subsequent storage, transportation, and application. Exemplarily, the isocyanate includes 4,4'-diphenylmethane diisocyanate (4,4'-MDI).

[0038] Preferably, the crosslinking agent is 0.3% to 0.5% of the total mass of isocyanate and polyether polyol, for example, 0.32%, 0.34%, 0.36%, 0.38%, 0.40%, 0.42%, 0.44%, 0.46%, or 0.48%.

[0039] Preferably, the crosslinking agent comprises trimethylolpropane.

[0040] Preferably, the mass ratio of polyvinyl alcohol to bentonite is (2~5):1, for example, 2.5:1, 3.0:1, 3.5:1, 4.0:1 or 4.5:1.

[0041] In this invention, the preferred mass ratio of polyvinyl alcohol to bentonite is (2~5):1, which balances the film-forming toughness and porosity barrier effect of the outer control layer. If the mass ratio of polyvinyl alcohol to bentonite is too low, the outer control coating liquid is prone to sagging, resulting in poor film formation; if the mass ratio of polyvinyl alcohol to bentonite is too high, the viscosity of the outer control coating liquid increases, easily leading to uneven spraying.

[0042] Preferably, the controlled-release fertilizer has a moisture content of ≤2%, such as 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, or 1.8%.

[0043] Preferably, the controlled-release fertilizer has a particle size of 2 to 4 mm, such as 2.2 mm, 2.4 mm, 2.6 mm, 2.8 mm, 3.0 mm, 3.2 mm, 3.4 mm, 3.6 mm or 3.8 mm.

[0044] Preferably, the thickness deviations of the base layer, inner control layer, and outer control layer are each independently within ±5 μm, such as ±1 μm, ±2 μm, ±3 μm, or ±4 μm.

[0045] In a second aspect, the present invention provides a method for preparing a controlled-release fertilizer as described in the first aspect, the method comprising sequentially coating the surface of a fertilizer core material with a base coating layer, an inner control layer and an outer control layer to obtain the controlled-release fertilizer.

[0046] Preferably, the preparation method includes the following steps: (1) mixing nitrogen fertilizer, phosphorus-potassium compound fertilizer, potassium fertilizer, silicon-calcium-magnesium fertilizer and optionally water-soluble binder, granulating to obtain fertilizer core material; (2) coating the fertilizer core material obtained in step (1) with a bottom coating liquid formed by mixing bio-based polyol, water and emulsifier to form a bottom coating layer; (3) mixing isocyanate, polyether polyol and crosslinking agent, reacting to form an inner control coating liquid, and then coating the bottom coating layer formed in step (2) with the inner control coating liquid to form an inner control layer; (4) mixing polyvinyl alcohol, bentonite and water to form an outer control coating liquid, and coating the inner control layer formed in step (3) with the outer control coating liquid to form an outer control layer, thereby obtaining the controlled-release fertilizer.

[0047] Preferably, the granulation in step (1) is carried out in a granulator, the granulation temperature is 60~70℃ (e.g. 61℃, 62℃, 63℃, 64℃, 65℃, 66℃, 67℃, 68℃ or 69℃, etc.), and the granulation speed is 30~40 r / min (e.g. 31 r / min, 32 r / min, 33 r / min, 34 r / min, 35 r / min, 36 r / min, 37 r / min, 38 r / min or 39 r / min, etc.).

[0048] Preferably, the particle size of the granulation is 2 to 4 mm, such as 2.2 mm, 2.4 mm, 2.6 mm, 2.8 mm, 3.0 mm, 3.2 mm, 3.4 mm, 3.6 mm or 3.8 mm.

[0049] Preferably, the granulation process further includes a drying step.

[0050] Preferably, the moisture content of the fertilizer core material is ≤2%, for example, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6% or 1.8%, etc.

[0051] Preferably, the mass ratio of the bio-based polyol and water in step (2) is (1~1.5):3, for example, 1.1:3, 1.2:3, 1.3:3 or 1.4:3, etc.

[0052] Preferably, the coating in step (2) includes coating by spraying a base coating liquid using a fluidized bed coating machine.

[0053] Preferably, the coating temperature in step (2) is 45~55℃ (e.g., 46℃, 47℃, 48℃, 49℃, 50℃, 51℃, 52℃, 53℃ or 54℃, etc.), the coating wind speed is 0.3~0.5 m / s (e.g., 0.32 m / s, 0.34 m / s, 0.36 m / s, 0.38 m / s, 0.40 m / s, 0.42 m / s, 0.44 m / s, 0.46 m / s or 0.48 m / s, etc.), and the coating time is 20~30 min (21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min or 29 min, etc.).

[0054] In this invention, the wind speed of the fluidized bed coating machine in step (2) is preferably 0.3~0.5 m / s for coating, which can make the fertilizer core material flow stably and uniformly in the fluidized bed, ensure that the bottom coating liquid can be uniformly attached to the surface of each fertilizer core material, and further ensure the consistency of the thickness of the formed bottom coating layer.

[0055] Preferably, the reaction temperature in step (3) is 55~65℃ (e.g., 56℃, 57℃, 58℃, 59℃, 60℃, 61℃, 62℃, 63℃ or 64℃, etc.), and the reaction time is 15~20 min (e.g., 15.0 min, 15.5 min, 16.0 min, 16.5 min, 17.0 min, 17.5 min, 18.0 min, 18.5 min, 19.0 min, 19.5 min or 20.0 min, etc.).

[0056] In this invention, the preferred temperature for the crosslinking reaction of isocyanate and polyether polyol in step (3) is 55~65℃. If the temperature is below 55℃, the reaction rate is too slow, and the degree of crosslinking of the crosslinking network is low or a longer reaction time is required within the reaction time. If the temperature is above 65℃, the reaction will be too fast and prone to "bursting polymerization", resulting in excessive crosslinking and increased brittleness of the inner control layer, which increases the risk of damage during subsequent storage and transportation. By controlling the reaction temperature of 55~65℃ and the reaction time of 15~20 min, sufficient crosslinking without excessive polymerization can be achieved, which can balance the density and flexibility of the inner control layer. This allows the nutrient release of the prepared slow-release fertilizer to remain relatively stable during the jointing stage, accurately matching the stable nutrient demand rhythm of rice at each stage.

[0057] Preferably, the coating in step (3) includes coating by spraying an internal control coating liquid using a fluidized bed coating machine.

[0058] Preferably, the coating temperature in step (3) is 55~65℃ (e.g., 56℃, 57℃, 58℃, 59℃, 60℃, 61℃, 62℃, 63℃ or 64℃, etc.), the coating wind speed is 0.4~0.6 m / s (e.g., 0.42 m / s, 0.44 m / s, 0.46 m / s, 0.48 m / s, 0.50 m / s, 0.52 m / s, 0.54 m / s, 0.56 m / s or 0.58 m / s, etc.), and the coating time is 30~40 min (e.g., 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min or 39 min, etc.).

[0059] In this invention, the wind speed of the coating in step (3) is preferably adjusted to 0.4~0.6 m / s. This is to adapt to the relatively higher viscosity of the inner control coating liquid, maintain the uniform fluidization of the fertilizer core material, and allow the inner control coating liquid to quickly form a film on the surface of the fertilizer core material, so as to ensure the stability of the density of the inner control layer.

[0060] Preferably, the coating in step (4) includes coating by spraying an external control coating liquid using a fluidized bed coating machine.

[0061] Preferably, the coating temperature in step (4) is 60~70℃ (e.g., 61℃, 62℃, 63℃, 64℃, 65℃, 66℃, 67℃, 68℃ or 69℃, etc.), the coating wind speed is 0.5~0.7 m / s (e.g., 0.52 m / s, 0.54 m / s, 0.56 m / s, 0.58 m / s, 0.60 m / s, 0.62 m / s, 0.64 m / s, 0.66 m / s or 0.68 m / s, etc.), and the coating time is 25~35 min (e.g., 26 min, 27 min, 28 min, 29 min, 30 min, 31 min, 32 min, 33 min or 34 min, etc.).

[0062] Preferably, the mass percentage of polyvinyl alcohol and bentonite in the external coating solution is 8% to 10% (e.g., 8.2%, 8.4%, 8.6%, 8.8%, 9.0%, 9.2%, 9.4%, 9.6%, or 9.8%, etc.).

[0063] In this invention, the mass percentage of polyvinyl alcohol and bentonite in the external control coating liquid is preferably 8%~10%, which can balance the spray flowability and film thickness of the external control coating liquid, avoiding the problems of spray blockage caused by excessively high concentration or excessively thin external control layer caused by excessively low concentration; while the wind speed is adjusted to 0.5~0.7 m / s to adapt to the viscosity characteristics of the external control coating liquid, ensuring that the fertilizer core material is fully fluidized in the fluidized bed, allowing the external control coating liquid to adhere evenly and form an aggregated textured structure with uniform pore distribution.

[0064] Preferably, the spraying described in steps (2), (3) and (4) each independently includes spraying by means of a spray, the spray pressure is 0.3~0.5 MPa (e.g. 0.32 MPa, 0.34 MPa, 0.36 MPa, 0.38 MPa, 0.40 MPa, 0.42 MPa, 0.44 MPa, 0.46 MPa or 0.48 MPa, etc.), and the spray flow rate is 5~8 mL / min (e.g. 5.3 mL / min, 5.6 mL / min, 5.9 mL / min, 6.2 mL / min, 6.5 mL / min, 6.8 mL / min, 7.1 mL / min, 7.4 mL / min or 7.7 mL / min, etc.).

[0065] Preferably, the spraying in steps (2), (3) and (4) is intermittent spraying.

[0066] In this invention, the spray pressure in steps (2), (3), and (4) is preferably 0.3~0.5 MPa, which allows the bottom coating liquid, inner control coating liquid, and outer control coating liquid to form uniform droplets with a diameter of 10~20 μm; while the spray flow rate of 5~8 mL / min is suitable for the coating time requirements of each layer of the bottom coating layer, inner control layer, and outer control layer; if the pressure is lower than 0.3 MPa, the droplet size is too large and it is easy to cause excessive local accumulation; if the pressure is higher than 0.5 MPa, the droplets are too fine and are easy to agglomerate in the fluidized bed, which wastes the coating liquid and causes uneven pore distribution; if the flow rate is lower than 5 mL / min, the coating time needs to be extended, and the production efficiency will be reduced; if the flow rate is higher than 8 mL / min, the interface bonding force between the layer structure or between the layer structure and the fertilizer core material will decrease due to the excessively fast droplet adhesion rate, which increases the risk of delamination; by controlling the pressure of 0.3~0.5 MPa and 5~8 mL / min, the coating time can be extended, and the production efficiency will be reduced. The flow rate of mL / min ensures the atomization uniformity of the bottom coating liquid, inner control coating liquid and outer control coating liquid in steps (2), (3) and (4), keeping the thickness deviation within ±5 μm. It also achieves tight bonding between the layer structures or between the layer structures and the fertilizer core material, while balancing production efficiency and the utilization rate of the coating material, further ensuring the performance consistency of different batches of products.

[0067] In this invention, the preparation method of the controlled-release fertilizer has clear process parameters and good reproducibility.

[0068] Preferably, step (4) after forming the outer control layer further includes drying and screening steps.

[0069] Preferably, the drying temperature is 70~80℃ (e.g., 71℃, 72℃, 73℃, 74℃, 75℃, 76℃, 77℃, 78℃ or 79℃, etc.), and the drying time is 1~2 h (e.g., 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h or 1.9 h, etc.).

[0070] In this invention, the drying temperature is preferably 70~80℃, which avoids the impact of excessively high temperature on the structural stability of the base coating, inner control layer and outer control layer (especially the aggregated texture of polyvinyl alcohol-bentonite in the outer control layer), and also ensures that the moisture content of the controlled-release fertilizer is maintained at ≤2%, preventing the components in the fertilizer core material from absorbing moisture and clumping during subsequent storage and transportation.

[0071] Preferably, the screening includes removing controlled-release fertilizers with a particle size of less than 2 mm and controlled-release fertilizers with a particle size of more than 4 mm.

[0072] In this invention, the process of screening out controlled-release fertilizers with particle sizes less than 2 mm and larger than 4 mm results in controlled-release fertilizers with particle sizes between 2 and 4 mm. This ensures that the finished fertilizer particles are of uniform size and that the nutrient release rhythm is consistent during application. On the other hand, it also removes particles that are not up to standard or may have incomplete coatings, thus ensuring the overall controlled-release performance of the product remains stable.

[0073] Thirdly, the present invention provides an application of the controlled-release fertilizer as described in the first aspect as a fertilizer for rice seedlings.

[0074] Compared with the prior art, the present invention has at least the following beneficial effects: The controlled-release fertilizer raw materials described in this invention are environmentally friendly, reducing the risk of environmental residues. They exhibit good interfacial compatibility between layers and high mechanical stability, minimizing nutrient "explosive release" caused by damage during storage, transportation, and application. This achieves a balance between nutrient utilization efficiency and environmental friendliness. The controlled-release fertilizer is tested for its slow-release effect using a continuous static water extraction method, with a release period of ≥49 days, and preferably up to 60 days. The controlled-release fertilizer is also tested for its slow-release effect using a soil culture method. Nitrogen release is low before day 10 (approximately during the rice seedling stage), increases from day 11 to day 30 (approximately during the rice tillering stage), reaching the first peak, stabilizes from day 31 to day 60 (approximately during the rice jointing stage), increases again from day 61 to day 90 (approximately during the rice heading and flowering stage), and reaches a second peak on day 90. The controlled-release fertilizer exhibits a peak nutrient release period, with a slight increase in nitrogen release during days 90-110 (approximately during the rice grain-filling stage), preventing nutrient deficiency. Utilizing a soil-cultivated slow-release process, this fertilizer is tailored to the nutrient requirements of rice growth, exhibiting a dual-peak nutrient release characteristic. This effectively prevents seedling burn during the seedling stage and nutrient deficiency during the heading, flowering, and grain-filling stages. Its long nutrient release period covers the critical nutrient requirements of rice, effectively contributing to improved seedling quality and the achievement of fertilizer reduction and efficiency goals in dry-land rice cultivation. Furthermore, the controlled-release fertilizer possesses excellent mechanical stability and particle size uniformity, making it suitable for large-scale storage, transportation, and field application. Attached Figure Description

[0075] Figure 1 Line graphs showing the cumulative nitrogen release rate obtained by testing the slow-release effect of the controlled-release fertilizers provided in Examples 1-5, Comparative Examples 1-4, Comparative Examples 6 and Comparative Examples 8-9 using the static water continuous extraction method. Figure 2 The chart shows a comparison of nitrogen release during specific time periods and cumulative nitrogen release obtained from the controlled-release fertilizers provided in Example 1 and Comparative Examples 3 to 6 using the soil culture method to test the controlled-release effect. Detailed Implementation

[0076] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0077] Unless otherwise specified, the materials and equipment involved in the following detailed embodiments are all conventional materials and equipment in the art and will not affect the technical effects of the present invention.

[0078] Unless otherwise specified, all reagents and raw materials used in the following examples and comparative examples are commercially available products. Some raw material information is as follows: Silicon-calcium-magnesium fertilizer: manufactured by Hengshui Gemei Trace Elements Co., Ltd.

[0079] Soybean oil-based polyol: hydroxyl value 193.97 mg KOH / g, manufacturer is Linyi Deken Smart Fertilizer Technology Co., Ltd.

[0080] Castor oil-based polyol: hydroxyl value 164 mg KOH / g, manufactured by Tianjin Kaitong Chemical Co., Ltd.

[0081] Polyether polyol: hydroxyl value 255 mg KOH / g, acid value 0.3897 mg KOH / g, viscosity 867 Pa·s, moisture content 0.37%, manufactured by Yantai Wanhua Polyurethane Co., Ltd.

[0082] Polyvinyl alcohol: Polyvinyl alcohol 2699, hydroxyl value 654 mg KOH / g, manufacturer is Inner Mongolia Shuangxin Environmental Protection Materials Co., Ltd.

[0083] Bentonite: Sodium-based bentonite, manufactured by Shizhong Mingzhi Chemical (Shanghai) Co., Ltd.; it was calcined at 800℃ for 2 h, 900℃ for 2 h, 1000℃ for 2 h, and 1100℃ for 2 h respectively to obtain bentonite calcined at 800℃, 900℃, 1000℃ and 1100℃ respectively.

[0084] Example 1 This embodiment provides a controlled-release fertilizer and its preparation method. The controlled-release fertilizer includes a fertilizer core material and a base coating, an inner control layer, and an outer control layer sequentially coated on the surface of the fertilizer core material. The total thickness of the base coating, inner control layer, and outer control layer is 245 μm, and the particle size of the controlled-release fertilizer is in the range of 2~4 mm. The preparation method includes the following steps: (1) Mix 40 kg of nitrogen fertilizer (urea), 20 kg of phosphorus-potassium compound fertilizer (potassium dihydrogen phosphate), 15 kg of potassium fertilizer (potassium chloride), 15 kg of silicon-calcium-magnesium fertilizer and 0.25 kg of sodium carboxymethyl cellulose, put them into a granulator for granulation, control the granulation temperature at 65℃ and the rotation speed at 35 r / min to form spherical particles with a particle size in the range of 2~4 mm, dry them at 80℃ to a moisture content of 1.8% to obtain fertilizer core material, in which the total mass percentage of N, P2O5 and K2O is 46.2%; The sphericity of the above granulation and the proportion of spherical particles with a diameter in the range of 2~4 mm were tested. The test results are shown in Table 1.

[0085] (2) A bottom coating solution is formed by mixing bio-based polyol (soybean oil-based polyol) and deionized water with emulsifier (Tween-80) in a mass ratio of 1:3. The mass of the emulsifier is 0.2% of the mass of the bio-based polyol. The fertilizer core material obtained in step (1) is placed into a fluidized bed coating machine. The bottom coating solution is sprayed onto the fertilizer core material by spraying in a fluidized bed coating machine. The temperature of the bed in the fluidized bed coating machine is 50℃, the wind speed is 0.4 m / s, the spraying is intermittent during the coating process, the spraying pressure is 0.4 MPa, the spraying flow rate is 6 mL / min, and the total time of the coating process is 25 min. A bottom coating layer is formed on the fertilizer core material with an average thickness of 65 μm.

[0086] (3) Isocyanate (4,4'-MDI) and polyether polyol with a molar ratio of 1.2:1 are mixed with crosslinking agent (trimethylolpropane). The mass of crosslinking agent is 0.4% of the total mass of isocyanate and polyether polyol. The mixture is stirred at 60°C for 18 min to form an inner control coating liquid. Then, the inner control coating liquid is sprayed onto the surface of the base layer formed in step (2) by spraying using a fluidized bed coating machine. The temperature of the bed in the fluidized bed coating machine is 60°C, the wind speed is 0.5 m / s, the spraying is intermittent during the coating process, the spray pressure is 0.4 MPa, the spray flow rate is 6 mL / min, and the total time of the coating process is 35 min to form an inner control layer with an average thickness of 100 μm.

[0087] (4) Mix polyvinyl alcohol and bentonite (calcined at 900℃) in a mass ratio of 3:1, add deionized water and stir to form an external control coating liquid. The mass percentage of polyvinyl alcohol and bentonite in the external control coating liquid is 9%. Then, use a fluidized bed coating machine to spray the surface of the internal control layer formed in step (3) to coat it. The temperature of the bed in the fluidized bed coating machine is 65℃, the wind speed is 0.6 m / s, the spraying is intermittent during the coating process, the spraying pressure is 0.4 MPa, the spraying flow rate is 6 mL / min, and the total time of the coating process is 30 min to form an external control layer with an average thickness of 80 μm.

[0088] (5) The coated granules are placed in a 75°C dryer and dried for 1.5 h. After cooling to room temperature, the granules with a particle size of 2-4 mm are screened to obtain the controlled-release fertilizer.

[0089] Example 2 This embodiment provides a controlled-release fertilizer and its preparation method. The controlled-release fertilizer includes a fertilizer core material and a base coating, an inner control layer, and an outer control layer sequentially coated on the fertilizer core material. The total thickness of the base coating, inner control layer, and outer control layer is 210 μm, and the particle size of the controlled-release fertilizer is in the range of 2-4 mm. The preparation method includes the following steps: (1) Mix 40 kg of nitrogen fertilizer (urea), 20 kg of phosphorus-potassium compound fertilizer (potassium dihydrogen phosphate), 15 kg of potassium fertilizer (potassium chloride), 15 kg of silicon-calcium-magnesium fertilizer and 0.20 kg of sodium carboxymethyl cellulose, put them into a granulator for granulation, control the granulation temperature at 60℃ and the rotation speed at 30 r / min to form spherical particles with a particle size in the range of 2~4 mm, dry them at 80℃ to a moisture content of 1.8% to obtain fertilizer core material, in which the total mass percentage of N, P2O5 and K2O is 46.2%; The sphericity of the above granulation and the proportion of spherical particles with a diameter in the range of 2~4 mm were tested. The test results are shown in Table 1.

[0090] (2) A bottom coating solution is formed by mixing bio-based polyol (castor oil-based polyol) and deionized water with emulsifier (Tween-80) in a mass ratio of 1:3. The mass of the emulsifier is 0.2% of the mass of the bio-based polyol. The fertilizer core material obtained in step (1) is placed into a fluidized bed coating machine. The bottom coating solution is sprayed onto the fertilizer core material by spraying in a fluidized bed coating machine. The temperature of the bed in the fluidized bed coating machine is 45℃, the wind speed is 0.3 m / s, the spraying is intermittent during the coating process, the spraying pressure is 0.3 MPa, the spraying flow rate is 5 mL / min, and the total time of the coating process is 20 min. A bottom coating layer is formed on the fertilizer core material with an average thickness of 55 μm.

[0091] (3) Isocyanate (4,4'-MDI) and polyether polyol with a molar ratio of 1.5:1 are mixed with crosslinking agent (trimethylolpropane). The mass of crosslinking agent is 0.4% of the total mass of isocyanate and polyether polyol. The mixture is stirred at 55°C for 20 min to form an inner control coating liquid. Then, the inner control coating liquid is sprayed onto the surface of the base layer formed in step (2) by spraying using a fluidized bed coating machine. The temperature of the bed in the fluidized bed coating machine is 55°C, the wind speed is 0.4 m / s, the spraying is intermittent during the coating process, the spray pressure is 0.3 MPa, the spray flow rate is 5 mL / min, and the total time of the coating process is 30 min to form an inner control layer with an average thickness of 85 μm.

[0092] (4) Mix polyvinyl alcohol and bentonite (calcined at 900℃) in a mass ratio of 2:1, add deionized water and stir to form an external control coating liquid. The mass percentage of polyvinyl alcohol and bentonite in the external control coating liquid is 8%. Then, use a fluidized bed coating machine to spray the surface of the inner control layer formed in step (3) to coat it. The temperature of the bed in the fluidized bed coating machine is 60℃, the wind speed is 0.5 m / s, the spraying is intermittent during the coating process, the spray pressure is 0.3 MPa, the spray flow rate is 5 mL / min, and the total time of the coating process is 25 min to form an external control layer with an average thickness of 70 μm.

[0093] (5) The coated granules are placed in a 75°C dryer and dried for 1.5 h. After cooling to room temperature, they are screened and granules with a particle size of 2-4 mm are retained to obtain the controlled-release fertilizer.

[0094] Example 3 This embodiment provides a controlled-release fertilizer and its preparation method. The controlled-release fertilizer includes a fertilizer core material and a base coating, an inner control layer, and an outer control layer sequentially coated on the fertilizer core material. The total thickness of the base coating, inner control layer, and outer control layer is 290 μm, and the particle size of the controlled-release fertilizer is in the range of 2-4 mm. The preparation method includes the following steps: (1) Mix 40 kg of nitrogen fertilizer (urea), 20 kg of phosphorus-potassium compound fertilizer (potassium dihydrogen phosphate), 15 kg of potassium fertilizer (potassium chloride), 15 kg of silicon-calcium-magnesium fertilizer and 0.23 kg of sodium carboxymethyl cellulose, put them into a granulator for granulation, control the granulation temperature at 70℃ and the rotation speed at 40 r / min, select spherical particles with a particle size in the range of 2~4 mm, dry them at 80℃ to a moisture content of 1.8%, and obtain fertilizer core material, in which the total mass percentage of N, P2O5 and K2O is 46.2%; The sphericity of the above granulation and the proportion of spherical particles with a diameter in the range of 2~4 mm were tested. The test results are shown in Table 1.

[0095] (2) A bottom coating solution is formed by mixing bio-based polyols (soybean oil-based polyols and castor oil-based polyols with a mass ratio of 1.5:3) and deionized water with emulsifier (Tween-80). The mass of the emulsifier is 0.18% of the mass of the bio-based polyols. The fertilizer core material obtained in step (1) is placed into a fluidized bed coating machine. The bottom coating solution is sprayed onto the fertilizer core material by spraying in a spraying manner. The temperature of the bed in the fluidized bed coating machine is 55℃, the wind speed is 0.5 m / s, the spraying is intermittent during the coating process, the spraying pressure is 0.5 MPa, the spraying flow rate is 8 mL / min, and the total time of the coating process is 30 min. A bottom coating layer with an average thickness of 80 μm is formed on the fertilizer core material.

[0096] (3) Isocyanate (4,4'-MDI) and polyether polyol with a molar ratio of 1.5:1 are mixed with crosslinking agent (trimethylolpropane). The mass of crosslinking agent is 0.4% of the total mass of isocyanate and polyether polyol. The mixture is stirred at 65°C for 15 min to form an inner control coating liquid. Then, the inner control coating liquid is sprayed onto the surface of the base layer formed in step (2) by spraying using a fluidized bed coating machine. The temperature of the bed in the fluidized bed coating machine is 65°C, the wind speed is 0.6 m / s, the spraying is intermittent during the coating process, the spray pressure is 0.5 MPa, the spray flow rate is 8 mL / min, and the total time of the coating process is 40 min to form an inner control layer with an average thickness of 115 μm.

[0097] (4) Mix polyvinyl alcohol and bentonite (calcined at 900℃) in a mass ratio of 5:1, add deionized water and stir to form an external control coating liquid. The mass percentage of polyvinyl alcohol and bentonite in the external control coating liquid is 8%. Then, use a fluidized bed coating machine to spray the surface of the internal control layer formed in step (3) to coat it. The temperature of the bed in the fluidized bed coating machine is 70℃, the wind speed is 0.7 m / s, the spraying is intermittent during the coating process, the spraying pressure is 0.5 MPa, the spraying flow rate is 8 mL / min, and the total time of the coating process is 35 min to form an external control layer with an average thickness of 95 μm.

[0098] (5) The coated granules are placed in a 75°C dryer and dried for 1.5 h. After cooling to room temperature, they are screened and granules with a particle size of 2-4 mm are retained to obtain the controlled-release fertilizer.

[0099] Example 4 This embodiment provides a controlled-release fertilizer and its preparation method. The difference between this embodiment and Embodiment 1 is that the mass of sodium carboxymethyl cellulose is adjusted to 0.15 kg, while other conditions are the same as in Embodiment 1.

[0100] Example 5 This embodiment provides a controlled-release fertilizer and its preparation method. The difference between this embodiment and Example 1 is that the mass of sodium carboxymethyl cellulose is adjusted to 0.30 kg, while other conditions are the same as in Example 1.

[0101] Comparative Example 1 This comparative example provides a controlled-release fertilizer and its preparation method. The difference between this and Example 1 is that the total thickness of the base layer, inner control layer and outer control layer is 163 μm. In the preparation method, the coating time in step (2) is shortened so that the average thickness of the base layer is 43 μm. In step (3), the coating time is shortened so that the average thickness of the inner control layer is 67 μm. In step (4), the coating time is shortened so that the average thickness of the outer control layer is 53 μm. Other conditions are the same as in Example 1.

[0102] Comparative Example 2 This comparative example provides a controlled-release fertilizer and its preparation method. The difference between this and Example 1 is that the total thickness of the base layer, inner control layer and outer control layer is 343 μm. In the preparation method, the coating time is extended in step (2) so that the average thickness of the base layer is 91 μm. In step (3) the coating time is extended so that the average thickness of the inner control layer is 140 μm. In step (4) the coating time is extended so that the average thickness of the outer control layer is 112 μm. Other conditions are the same as in Example 1.

[0103] Comparative Example 3 This comparative example provides a controlled-release fertilizer and its preparation method. The difference between this and Example 1 is that it does not include an inner control layer and an outer control layer. The average thickness of the base coating is 245 μm. The preparation method does not include steps (3) and (4). In step (2), the total time of the coating process is extended so that the average thickness of the base coating reaches 245 μm. Other conditions are the same as in Example 1.

[0104] Comparative Example 4 This comparative example provides a controlled-release fertilizer and its preparation method. The difference between this and Example 1 is that it does not include an outer control layer, the average thickness of the base layer is 96.5 μm and the average thickness of the inner control layer is 148.5 μm, the preparation method does not include step (4), and the total time of the coating process in steps (2) and (3) is extended so that the average thickness of the formed base layer reaches 96.5 μm and the average thickness of the inner control layer reaches 148.5 μm. Other conditions are the same as in Example 1.

[0105] Comparative Example 5 This comparative example provides a controlled-release fertilizer and its preparation method. The difference between this and Example 1 is that it does not include the base layer and the inner control layer, the thickness of the outer control layer is 245 μm, the preparation method does not include steps (2) and (3), and the total time of the coating process is extended in step (4) so ​​that the average thickness of the formed outer control layer is 245 μm. Other conditions are the same as in Example 1.

[0106] Comparative Example 6 This comparative example provides a slow-release fertilizer, which is a commercially available bio-based slow-release fertilizer specifically for rice, with a controlled-release period of 60 days. Bio-based refers to plant oil-based fertilizer.

[0107] Comparative Example 7 This comparative example provides a fertilizer, wherein the fertilizer is superphosphate and potassium chloride in a mass ratio of 5:1.

[0108] Comparative Example 8 This comparative example provides a slow-release fertilizer and its preparation method. The difference between this example and Example 1 is that the bentonite calcined at 900°C is replaced with the same mass of uncalcined bentonite, while the other conditions are the same as in Example 1.

[0109] Comparative Example 9 This comparative example provides a slow-release fertilizer and its preparation method. The difference between this and Example 1 is that the bentonite calcined at 900°C is replaced with the same mass of bentonite calcined at 1100°C, while the other conditions are the same as in Example 1.

[0110] Performance testing (1) Particle pressure strength: The particle pressure strength of the controlled-release fertilizer was tested using a particle pressure tester FT-9=803.

[0111] (2) The nutrient release effect of slow-release fertilizer was determined by static water continuous extraction method: the determination was carried out in accordance with HG / T 4216-2011 "Rapid detection method for nutrient release period and release rate of slow-release / controlled-release fertilizer".

[0112] Extraction: Weigh 10g of sample and place it in a 250mL Erlenmeyer flask with a stopper. Accurately add 200mL of water, gently shake to ensure the sample is completely submerged in water, tighten the stopper, and incubate the Erlenmeyer flask at 25℃. At the determined nutrient release point, remove the Erlenmeyer flask, filter all the liquid, shake well, and obtain the test solution for that nutrient release point. Continue to add 200mL of water to the Erlenmeyer flask and incubate until the next test point. Repeat the process, filtering all the liquid and shaking well to obtain the test solution for the next nutrient release point.

[0113] The above nutrient release points refer to the number of days of continuous extraction treatment, which are 1 day, 3 days, 5 days, 7 days, 10 days, 13 days, 16 days, 19 days, 22 days, 25 days, 28 days, 35 days, 42 days, 49 days, 56 days, 60 days and 70 days respectively. The nutrient release points can be increased or decreased according to the actual situation when different samples are tested. When the cumulative nitrogen release rate reaches (79±3)%, the extraction can be terminated. Each sample is tested 3 times and the average value is taken.

[0114] Calculation of cumulative nitrogen release rate: Measure the urea content in the test solution at each nutrient release point, calculate its mass fraction of urea in the controlled-release fertilizer, which is the nitrogen release rate at that nutrient release point, and calculate the cumulative nitrogen release rate.

[0115] (3) The soil culture method was used to determine the nutrient release effect of slow-release fertilizer.

[0116] A 1 mm thick nylon mesh was pressed into a mesh bag 4 cm long and 4 cm wide. 2.0g of the slow-release fertilizer prepared in Example 1 and Comparative Examples 3-6 were weighed out respectively. The controlled-release fertilizer was placed into a mesh bag to make a sample bag. The controlled-release fertilizer was spread out naturally and the initial mass was weighed. 150g of soil was put into a container, the surface was leveled, the sample bag was laid flat, and then 100g of soil was covered. The sample bag was incubated at a temperature of 25℃ and a humidity of 70% at field capacity. A series of sample bags were sampled and tested on days 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110 and 120. The coated fertilizer granules were sieved out, washed clean, dried and crushed. CO(NH2)2-N was determined by the dimethylaminobenzaldehyde colorimetric method. The cumulative nitrogen release was calculated by the difference method, and the nitrogen release during the period was also calculated. Each sample was tested three times and the average value was taken.

[0117] (4) Field application effect experiment of rice The experiment was conducted on Caifeng Street, Mashan Town, Jingzhou District, Jingzhou City, Hubei Province. The basic physicochemical properties of the tested soil were: pH=6.90, organic matter content: 18.30 g / kg, total nitrogen content: 5.40 g / kg, available phosphorus content: 29.10 mg / kg, and available potassium content: 189.10 mg / kg.

[0118] The rice variety used in the experiment was Yongyou 4949. Transplanting was conducted on May 14, 2025, and harvesting was on October 13, 2025. The experiment was conducted using a field plot with a plot area of ​​50m². 2 (10 m long, 5 m wide).

[0119] The experiment included three fertilization treatment samples: Fertilization treatment sample 1 was a single application of the slow-release fertilizer provided in Example 1 as base fertilizer, with an application rate of 675 kg·hm².-2 ; Fertilizer treatment sample 2 was treated with the slow-release fertilizer provided in comparative example 6 as base fertilizer, with an application rate of 600 kg·hm². -2 Then, on the 30th day, apply urea (46% nitrogen content) at a rate of 187.50 kg·hm². -2 On day 90, apply 105 kg·hm² of urea (46% nitrogen content) as a top dressing. -2 Fertilizer treatment sample 3 was treated with a single application of the fertilizer provided in comparative example 7 as basal fertilizer, with a superphosphate application rate of 750 kg·hm². -2 The application rate of potassium chloride is 150 kg·hm². -2 ; of which hm -2 The unit is hectares. The total nutrient input in fertilization treatment sample 1, fertilization treatment sample 2, and fertilization treatment sample 2 is shown in Table 3.

[0120] The above fertilization treatments all adopted the method of simultaneous side-deep fertilization during machine transplanting. Each fertilization treatment sample was made into 3 parallel samples. The plots were arranged in randomized block design. The field plots were planted according to the local farmers' usual transplanting density, with row spacing × hole spacing = 30cm × 10cm.

[0121] At maturity, three observation points were surveyed in each plot, with 100 hills surveyed at each point. The number of effective panicles was calculated, and 10 representative plants were selected based on the average number of panicles to determine the number of grains per panicle, the seed setting rate, and the thousand-grain weight. At harvest, 100 hills with uniform growth were harvested from each point to measure the actual yield.

[0122] Nitrogen fertilizer agronomical efficiency (NAE) = (yield in nitrogen-fertilized area - yield in nitrogen-free area) / nitrogen application rate.

[0123] Nitrogen fertilizer partial productivity (NPFP) = Yield of nitrogen-fertilized area / Amount of nitrogen applied.

[0124] Seed setting rate (SR) = Number of filled grains / (Number of filled grains + Number of empty grains) × 100%.

[0125] The test results are shown in Tables 1, 2, 3 and 4.

[0126] Table 1 In Table 1, " / " indicates that the test was not performed.

[0127] Table 2 In Table 2, " / " indicates that the test was not performed.

[0128] Table 3 In Table 3, " / " indicates that the nutrient was not added.

[0129] Table 4 In Table 4, " / " indicates that the test was not performed.

[0130] The cumulative nitrogen release, nitrogen release over a specific period, and nitrogen release rate reflect the cumulative nutrient release, nutrient release over a specific period, and nutrient release rate, respectively, according to Tables 1-4 and... Figures 1-2 Test results show that the nutrient release period of the controlled-release fertilizers provided in Examples 1 to 5, tested by the static water continuous extraction method, can reach more than 49 days. In the soil culture method test, the nutrient release of the controlled-release fertilizers in the initial period is relatively low, which can effectively avoid seedling burn. Nutrient release shows a double-peak characteristic, with the double peaks located at two stages where the nutrient demand of rice increases, perfectly matching the key nutrient requirement stages of rice. The controlled-release fertilizers have high particle pressure strength and good mechanical stability.

[0131] Compared to Example 1, if the mass percentage of water-soluble binder in the fertilizer core material is too low (Example 4), the bonding force between the raw materials of the fertilizer core material is insufficient, the fertilizer core material is easy to loosen, the pelleting rate is less than 80%, the particle pressure strength of the resulting controlled-release fertilizer decreases, the mechanical stability is low, and the nutrient release period tested by the static water continuous extraction method of the controlled-release fertilizer is shortened. If the mass percentage of water-soluble binder in the fertilizer core material is too high (Example 5), the fertilizer core material particles are large and easy to stick together, the pelleting rate will also decrease, and the texture will be hard due to excessive adhesion. This not only increases the energy consumption of granulation, but also reduces the adhesion between the coating layer composed of the subsequent base layer, inner control layer and outer control layer and the fertilizer core material, resulting in a decrease in the particle pressure strength of the controlled-release fertilizer and a shortened nutrient release period tested by the static water continuous extraction method of the controlled-release fertilizer. Therefore, it is better to select a water-soluble binder in the fertilizer core material with a mass percentage of 0.2% to 0.3%, which can keep the pelleting rate of the fertilizer core material stable at over 90%, and ensure that the proportion of fertilizer core material particles with a particle size of 2 to 4 mm is over 95%, thus guaranteeing the structural stability of the controlled-release fertilizer.

[0132] Comparison of Examples 1 to 5 shows that when the total thickness of the base layer, inner control layer and outer control layer is 240 to 300 μm, and the mass percentage of water-soluble binder in the fertilizer core material is controlled at 0.2% to 0.3%, the nutrient release period of the controlled-release fertilizer tested by the static water continuous extraction method can reach 60 days.

[0133] Compared with Example 1, if the total thickness of the base layer, inner control layer and outer control layer is too thin (Comparative Example 1), the blocking ability is insufficient, the nutrient release period tested by the static water continuous extraction method is shortened, and the cumulative nitrogen release in the first to 100 days is higher when the soil culture method is used to measure the nutrient release effect of the slow-release fertilizer, all of which indicate that the problem of nutrient depletion in the later stage is likely to occur.

[0134] Compared with Example 1, if the total thickness of the base layer, inner control layer and outer control layer is too thick (Comparative Example 2), the resistance to nutrient diffusion is too large, the nutrient release is too slow in the static water continuous extraction test, the nutrient release period is long, and when the soil culture method is used to measure the nutrient release effect of slow-release fertilizer, the peak of the second nitrogen release period is delayed until the 120th day, which does not match the nutrient requirement cycle of rice growth, and there is a risk of nutrient deficiency during the heading and flowering period.

[0135] Compared to Example 1, if the total thickness of the layer structure covering the fertilizer core material remains unchanged, and the controlled-release fertilizer does not have an inner control layer and an outer control layer (Comparative Example 3), then as follows: Figure 2 The initial nutrient release is too rapid, as shown in the figure. Figure 1 The short nutrient release period shown can easily lead to seedling burn in rice and nutrient deficiency during the heading and flowering stages. If the total thickness of the layers covering the fertilizer core remains unchanged, and the controlled-release fertilizer does not have an outer control layer (Comparative Example 4), then... Figure 2 The initial nutrient release is too rapid, as shown in the figure. Figure 1 The short nutrient release period shown can easily lead to seedling burn in rice and nutrient deficiency during heading and flowering. If the total thickness of the layers covering the fertilizer core remains unchanged, and the controlled-release fertilizer does not have a base layer and inner control layer, but the thickness of the outer control layer is adjusted to 245 μm (Comparative Example 5), then... Figure 2 The initial nutrient release is too rapid, as shown in the figure. Figure 1 The nutrient release period shown is short. This indicates that by combining the base coating, inner control layer, and outer control layer, the resulting slow-release fertilizer has a suitable nutrient release period that matches the nutrient requirements of rice growth.

[0136] Compared with Example 1, although the nutrient release period of commercially available slow-release fertilizers (Comparative Example 6) is not too short, the rapid release of nutrients in the early stage can easily lead to seedling burn in rice.

[0137] Compared to Example 1, if uncalcined bentonite (Comparative Example 8) is used, the bentonite tends to settle during the preparation of the external control coating solution, leading to stratification of the solution and easy clogging of the nozzle during spraying. The resulting controlled-release fertilizer has low particle pressure strength. The uncalcined bentonite has poor pore structure stability and adsorption performance, resulting in a short nutrient release period. Figure 1 As shown, late-stage nutrient deficiency is likely to occur; if the calcination temperature of the bentonite used is too high (Comparative Example 9), the outer control layer formed after the coating liquid is formed will be loose and porous, resulting in a decrease in the particle pressure strength of the controlled-release fertilizer, a weakening of the nutrient control performance, poor slow-release effect, and a short nutrient release period, such as... Figure 1 As shown, it can be seen that the slow-release fertilizer prepared by using bentonite calcined at 800~1000℃ has better performance.

[0138] Depend on Figure 2As can be seen, the controlled-release fertilizer provided in Example 1, tested for its slow-release effect using a soil culture method, showed that nitrogen release was lower before day 10, effectively preventing seedling burn. From day 11 to day 30, nitrogen release gradually increased, reaching the first nutrient release peak, meeting the nutrient requirements of rice during the tillering stage. From day 31 to day 60, nitrogen release was relatively stable. From day 61 to day 90, nitrogen release increased, reaching the second nutrient release peak, meeting the nutrient requirements of rice during the heading and flowering stage. From day 90 to day 120, nitrogen release was relatively high, increasing slightly, effectively preventing nutrient deficiency.

[0139] In the field application effect experiment of rice, compared with the fertilization treatment sample 2, the total nutrient input of the fertilization treatment sample 1 was reduced by 5.91%, but the number of effective grains per panicle, the number of grains per panicle, the thousand-grain weight, the seed setting rate, the yield, the agronomical utilization rate of nitrogen fertilizer, and the partial productivity of nitrogen fertilizer were all improved, indicating that the slow-release fertilizer created by this invention is superior to commercially available bio-based slow-release fertilizer for rice.

[0140] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A controlled-release fertilizer, characterized in that, The controlled-release fertilizer comprises a fertilizer core material and a base coating, an inner control layer, and an outer control layer sequentially coated on the surface of the fertilizer core material; the base coating comprises a bio-based polyol; the inner control layer comprises polyurethane; and the outer control layer comprises polyvinyl alcohol and bentonite. The bentonite includes bentonite calcined at 800~1000℃; The total thickness of the base layer, inner control layer and outer control layer is 200~300 μm.

2. The controlled-release fertilizer according to claim 1, characterized in that, The fertilizer core material comprises the following components: nitrogen fertilizer, phosphorus-potassium compound fertilizer, potassium fertilizer, and silicon-calcium-magnesium fertilizer; The total nutrient content of the fertilizer core material is ≥45%; The nitrogen fertilizer includes urea; The phosphorus-potassium compound fertilizer includes potassium dihydrogen phosphate; The potassium fertilizer includes potassium chloride.

3. The controlled-release fertilizer according to claim 2, characterized in that, The fertilizer core material also includes a water-soluble binder; The water-soluble binder includes sodium carboxymethyl cellulose; The water-soluble binder in the fertilizer core material has a mass percentage of 0.2% to 0.3%. The fertilizer core material is spherical in shape.

4. The controlled-release fertilizer according to claim 1, characterized in that, The fertilizer core material comprises the following components by weight: 40-45 parts nitrogen fertilizer, 20-25 parts phosphorus-potassium compound fertilizer, 10-15 parts potassium fertilizer, and 10-15 parts silicon-calcium-magnesium fertilizer. The average thickness of the base coating is 50~80 μm; The average thickness of the inner control layer is 80~120 μm; The average thickness of the outer control layer is 60~100 μm.

5. The controlled-release fertilizer according to claim 1, characterized in that, The base coating also includes an emulsifier; The emulsifier is present in an amount of 0.125% to 0.25% of the bio-based polyol. The emulsifier includes Tween-80; The bio-based polyols include soybean oil-based polyols and / or castor oil-based polyols; The raw materials for preparing the polyurethane include isocyanate, polyether polyol and crosslinking agent; The molar ratio of isocyanate to polyether polyol is (0.9~1.5):1; The crosslinking agent is 0.3% to 0.5% of the total mass of isocyanate and polyether polyol; The crosslinking agent includes trimethylolpropane; The mass ratio of polyvinyl alcohol to bentonite is (2~5):

1.

6. A method for preparing a controlled-release fertilizer as described in any one of claims 1 to 5, characterized in that, The preparation method includes sequentially coating the surface of the fertilizer core material with a base coating, an inner control layer, and an outer control layer to obtain the controlled-release fertilizer.

7. The preparation method according to claim 6, characterized in that, The preparation method includes the following steps: (1) Mix nitrogen fertilizer, phosphorus-potassium compound fertilizer, potassium fertilizer, silicon-calcium-magnesium fertilizer and water-soluble binder, granulate, and obtain fertilizer core material; (2) A bottom coating liquid is formed by mixing bio-based polyol, water and emulsifier. The bottom coating liquid is used to coat the surface of the fertilizer core material obtained in step (1) to form a bottom coating layer. (3) Mix isocyanate, polyether polyol and crosslinking agent, react to form internal control coating liquid, and then coat the surface of the base coating layer formed in step (2) with the internal control coating liquid to form an internal control layer; (4) Mix polyvinyl alcohol, bentonite and water to form an external control coating liquid. Coat the surface of the inner control layer formed in step (3) with the external control coating liquid to form an external control layer and obtain the slow-release fertilizer.

8. The preparation method according to claim 7, characterized in that, The granulation in step (1) is carried out in a granulator at a temperature of 60-70°C and a rotation speed of 30-40 r / min. The granulation process also includes a drying step. The moisture content of the fertilizer core material is ≤2%; The mass ratio of bio-based polyol to water in step (2) is (1~1.5):3; The coating process in step (2) includes coating by spraying a base coating liquid using a fluidized bed coating machine; The temperature of the coating in step (2) is 45~55℃, the wind speed of the coating is 0.3~0.5 m / s, and the coating time is 20~30 min; The reaction temperature in step (3) is 55~65℃, and the reaction time is 15~20 min; The coating process in step (3) involves spraying an internal control coating solution using a fluidized bed coating machine. The temperature of the coating in step (3) is 55~65℃, the wind speed of the coating is 0.4~0.6 m / s, and the coating time is 30~40 min; The coating process in step (4) includes coating by spraying an externally controlled coating solution using a fluidized bed coating machine; The temperature of the coating in step (4) is 60~70℃, the wind speed of the coating is 0.5~0.7 m / s, and the coating time is 25~35min; The mass percentage of polyvinyl alcohol and bentonite in the external coating solution is 8%~10%; The spraying described in steps (2), (3) and (4) each independently includes spraying by spraying, with the spray pressure being 0.3~0.5MPa and the spray flow rate being 5~8 mL / min. The spraying described in steps (2), (3) and (4) is intermittent spraying.

9. The preparation method according to claim 7, characterized in that, Step (4) after forming the outer control layer also includes drying and screening steps; The drying temperature is 70~80℃, and the drying time is 1~2 hours.

10. The application of a controlled-release fertilizer as described in any one of claims 1 to 5 as a fertilizer for rice seedlings.

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