Regarding the caking issue with top-dressing fertilizers

Generally, for fertilizers that are severely clumped, it is necessary to apply oil and sprinkle powder simultaneously in order to remove moisture, lower the temperature, prevent deliquescence and the formation of crystal bridges, and then seal the mixture to block moisture from entering...............................

Caking and anti-caking of compound fertilizers Shanghai Keyi Fertilizer Engineering Technology Center Chen Mingliang, Liang Ji, Jiang Jianguo As compound fertilizers evolve from lower to higher concentrations, their production volume and variety increase year by year; the concentration per unit of these fertilizers rises, which in turn leads to an increase in the content of nitrogen, phosphorus, and potassium in them. In other words, the salt concentration in the fertilizers increases, and their chemical composition also changes. Along with the formation of double salts in the product and the phase changes associated with crystallization, and due to the influence of external conditions during storage, fertilizers tend to compact and form lumps; severe lumping can affect the application of the fertilizer. The caking problem in compound fertilizers has always been a concern for the fertilizer industry; it is also one of the key factors affecting the quality of domestically produced fertilizers. The clumping problem not only causes difficulties in storage and transportation for fertilizer manufacturers, but more seriously, it poses significant inconvenience to users when using the fertilizers. The reason why the price of imported compound fertilizers is **higher than that of domestic ones is, apart from people’s preference for foreign products, mainly due to a difference in quality. This difference does not relate to the nutrient content of the products, but rather to their appearance, especially in terms of their clumping property. 1. Causes of caking Caking is a property in which a substance changes from a loose state to a compact mass or lump. This transformation can occur in both crystalline and amorphous substances, and every product has a tendency to caking. It is generally believed that fertilizer caking is caused by its internal properties, forming at the contact points of the particles. The mechanism behind caking is highly complex, and no complete and unified theory has yet been established; different caking theories offer various explanations for the causes of caking. Currently, the main theories include the crystal bridge theory, capillary adsorption theory, chemical interaction theory, and plastic deformation theory. The crystal bridge theory suggests that due to internal factors such as the properties of the material, its chemical composition, particle size, particle size distribution, and geometric shape, as well as external factors like humidity, temperature, pressure, and impurities, the presence of water within the material causes the surface of the material to dissolve and recrystallize. This leads to the formation of crystal bridges at the points where the crystal grains come into contact with each other. Over time, these crystal bridges cause the grain particles to stick together, gradually forming large aggregates. The capillary adsorption theory suggests that due to the capillary adsorption forces between the fine grains, the saturated vapor pressure at the capillary meniscus is lower than that in the surrounding environment, which creates conditions for water vapor to diffuse between the grains ； Hygroscopic fertilizers absorb moisture above their critical relative humidity, forming a saturated solution film on the surface of the crystals. This solution film accelerates capillary adsorption, and the meniscus created by surface tension causes ions to move toward the contact points between particles, resulting in cross-linking and agglomeration of adjacent particles. The chemical reaction theory suggests that fertilizers cannot react completely during the granulation process, and they continue to react during storage, forming double salts; the results of these reactions lead to recrystallization and caking. The theory of plastic deformation holds that fertilizer caking is always accompanied by deformation, and this deformation is intensified under pressure. The residual heat from the unfrozen fertilizer moves from the center of the particles outward; when these fertilizer particles are compressed, it leads to deformation and thus caking. 2. Factors affecting the caking of compound fertilizers There are many factors that influence the caking of compound fertilizers, the main ones being: (1) the chemical composition of the compound fertilizer ； (2) Hygroscopic properties of compound fertilizer components and humidity of the surrounding environment ； (3) Moisture content of the product ； (4) Temperature (5) Shape of particles and uniformity of particle size ； (6) Compressive strength of particles ； (7) Packing pressure during storage and transportation ； (8) Storage time ； (9) Content of impurities. (1) Chemical composition of compound fertilizers The composition of the raw materials is an internal factor that affects fertilizer caking. The raw materials used in the production of compound fertilizers include urea, *ao acid an, ammonium chloride, ammonium bicarbonate, monoammonium phosphate, diammonium phosphate, heavy calcium carbonate, superphosphate, potassium chloride, potassium sulfate, etc.; all of these materials have varying degrees of hygroscopicity. When different raw materials are mixed together, the critical moisture absorption point of the mixture decreases significantly compared to that of the individual substances, making it more susceptible to absorbing moisture. In the presence of water, chemical reactions can occur between certain ingredient components, resulting in complex salts and solid solutions. For example: NH4NO3 + KCl → KNO3 + NH4Cl; (NH4)2HPO4 + 2KNO3 → (NH4·K)HPO4 + (K·NH4)(NO3)2. These reactions can continue to occur in the finished products after packaging. During storage, such chemical reactions on the surface of the particles can very easily lead to the formation of crystal bridges. Therefore, when producing compound fertilizers, it is necessary to fully understand the compatibility among various raw materials, and pre-treatment may be carried out if needed; for example, pre-treating superphosphate to control reactions that could release crystalline water within the compound fertilizer and thus prevent caking. Another reason for caking due to chemical reactions is the change in the crystal structure of certain substances when there are sudden temperature changes. For example, in the case of *ao acid an, at 32.1°C and 84.2°C, its volume changes as its crystal structure changes, accompanied by the absorption or release of energy. Therefore, it is highly necessary to package and store the *ao acid an compound fertilizer after it has been fully cooled. (2) Hygroscopicity and environmental humidity: When moisture is absorbed by the particle surface, a saturated solution is formed quite quickly. Thereafter, as the moisture evaporates or is absorbed by other dry particles, the dissolved components precipitate and crystallize. As a result, a process of dissolution and recrystallization continues on the particle surface, leading to the formation of crystal bridges that cause caking. The critical relative humidity varies depending on the composition of the fertilizer; the critical relative humidity of a mixture of two or more types of basic fertilizers is usually lower than that of any individual fertilizer. For example, at 30°C, the critical relative humidity for a mixture of *ao acid and urea is only 18%; therefore, in the production of compound fertilizers, it is advisable to avoid using these two types of fertilizer together. In production, attention should be paid to the impact of environmental humidity. When packaging compound fertilizers, woven bags with durable lining films should be used, and it is best to fold and sew the seams. (3) Moisture content of the product: Moisture is the main factor affecting fertilizer caking. Any caking mechanism is related to the liquid phase content in the fertilizer. On the one hand, the presence of moisture leads to capillary bonding and the formation of crystal bridges ； On the other hand, moisture causes the fertilizer particles to soften, and under pressure they deform, increasing the contact area between the particles and thereby enhancing the strength of the bonds between them. There are mainly two sources of moisture: one is the residue from fertilizers used in production, which is forced to the surface of the particles under pressure ； The second source is the surrounding air, that is, the increase in the moisture content of fertilizers through moisture absorption. The reasons for moisture absorption can be summarized in two points: capillary condensation and a decrease in vapor pressure. Capillary condensation is caused by changes in the saturated vapor pressure at curved liquid surfaces. According to the Kelvin equation: ln(pr/p0) = k/r, where pr is the vapor pressure of the liquid on the surface ； p0— Vapor pressure of a planar liquid ； r — radius of curvature of the liquid surface ； k — a constant, which is fixed for a liquid substance at a certain temperature. It can be seen that the vapor pressure of a liquid is related to the shape and radius of curvature of its surface. P_concave ＜ P0 ＜ P_convex. Since the moisture between the particles forms a concave liquid surface, its saturated vapor pressure is lower than that of a flat liquid surface; as a result, water vapor in the air can easily reach saturation there, leading to vapor condensation. The decrease in vapor pressure occurs because the inorganic salts on the particle surface dissolve in the adsorbed water to form a saturated solution, whose vapor pressure is lower than that of pure water; when the water vapor pressure in the air exceeds this value, moisture absorption takes place. The moisture contained within the fertilizer particles promotes dissolution and recrystallization on the surface of the powder, resulting in the formation of crystal bridges in the pores of the powder. Over time, these crystals combine with each other, gradually forming lumps. Secondly, it is impossible for fertilizers to undergo complete reaction during the production process; due to thermal effects, chemical reactions continue to occur within the fertilizer. At this point, trace amounts of solution are present in the fertilizer, causing the crystals to dissolve and then redeposit, which results in the formation of crystal salt bridges that lead to clumping of the fertilizer. Therefore, requirements for the allowable water content (free water) in finished fertilizers have been established for different compositions and contents of fertilizers. The lower the moisture content of the particles, the less likely they are to clump together. Generally speaking, fertilizers with a high nitrogen content require a higher degree of drying, especially those that are compound fertilizers containing phosphoric acid or urea. The maximum moisture content limit for granular fertilizers commonly used internationally is shown in Appendix 1. Table 1: Maximum moisture content limits for granular fertilizers. Sequence Number, Fertilizer Type, Moisture Content/%: 1, 2, 3, 4, 5, 6, 7, 8. *AO acid, AN urea, sulfuric acid. Mixed fertilizers with N:P2O5 ratio ≥1:1, containing urea or *AO acid; mixed fertilizers with N:P2O5 ratio <1:1, containing urea or *AO acid; mixed fertilizers with N:P2O5 ratio ≥1:1, not containing urea or *AO acid; mixed fertilizers with N:P2O5 ratio <1:1, not containing urea or *AO acid. Mixed fertilizers containing small amounts of nitrogen fertilizer or none at all: 0–0.5, 0–0.5, 0–0.5, 0.5–1.0, 1.0–1.5, 1.5–2.5, 1.5–2.0, >2.0. (4) Temperature: The impact of temperature on caking is mainly reflected in packaging and storage. Packaging temperature has a particularly significant effect on caking; if the temperature is too high during packaging, the inorganic salts dissolved in the residual moisture will crystallize during cooling, forming salt bridges. For example, in the case of *ao acid an, if the temperature during packaging is 70°C and the moisture content is 1%, then when cooled to 10°C, more than 35 kg of crystals can precipitate from 1 ton of the product. This means that sufficient crystal bridges will form, leading to severe caking; therefore, the material should be thoroughly cooled before packaging. For fertilizers that are packaged directly, high temperatures can damage the packaging material; generally, it is necessary to cool them to below 54°C before packaging. The higher the storage temperature of fertilizers, the more likely they are to clump. During storage, if there are temperature changes, this, in the presence of moisture, will cause repeated dissolution and crystallization, thereby promoting the formation of crystal bridges ； On the other hand, it can also cause physicochemical changes in certain substances, such as crystal phase transitions. For this reason, the fertilizer must be cooled before it is packaged or sent to a bulk storage facility. *The storage temperature for AO acid AN and compound fertilizers containing AO acid AN should be below 54°C. Ammonium phosphate, ammonium phosphide sulfide, or urea – substances such as ammonium phosphate only require cooling to 71°C. The maximum storage temperature mentioned here refers to the condition where the material is dried to a specified moisture content; as the moisture content increases, the storage temperature becomes more sensitive to caking. (5) Particle shape: If the roundness of the product particles is poor or if fine powder is present, the contact area between the particles increases, leading to caking. Relatively larger particles that do not contain fine powder will reduce the contact points between particles, thereby tending to decrease caking. If the powder particles contain moisture, it facilitates solid dissolution and crystallization, leading to easier caking of the fertilizer; therefore, production standards for granular fertilizers specify requirements regarding the content of acceptable particles. (6) Compressive strength of particles: If the hardness or mechanical strength of the particles is low, they are prone to deformation and fragmentation during transportation and storage. The fine powder resulting from this increases the number of contact points between the particles, thereby facilitating caking. (7) Storage pressure: Increasing the storage pressure raises the likelihood of particle deformation and the contact area between particles, thereby increasing the possibility of crystal cross-linking and consequently the risk of caking. Fertilizers that tend to cake should generally not be piled up too high. For example, in the case of fertilizer packaged in 50kg units, when 20 packs are stacked together, the pressure exerted on the bottom pack is 0.35 kg/cm2. Fertilizers that do not clump together can be stacked in 30 packs or more. The average pressure at the bottom of a conical fertilizer pile in a bulk storage area can be calculated as hd/3. Here, d is the bulk density of the fertilizer in kg/m3, and h is the pile height in m. The pressure on the slant side of the conical pile is zero, while the maximum pressure at the center of the base is 2hd/3. (8) Storage time: The longer the storage time, the more times the recrystallization-dissolution process of the salt solution on the surface of the fertilizer occurs. Under constant pressure over an extended period, the fertilizer undergoes greater deformation, and the tendency to clump together becomes more pronounced. Therefore, the storage time of fertilizers should be shortened as much as possible. (9) Impurities and content: High-concentration compound fertilizers are more prone to caking than low-concentration ones. Adding water-insoluble inert substances when producing high-concentration compound fertilizers can reduce the bonding force between crystal bonds and minimize caking. For example, adding more than 5% of inert materials such as attapulgite powder, porcelain clay, or fly ash to the raw materials can **reduce the likelihood of caking. In fact, it is difficult to determine exactly which factor causes caking; fertilizer caking is usually the result of the combined action of various factors. 3. Mechanism of action of anti-caking agents: The caking of fertilizers is caused by various factors. Therefore, in fertilizer production, efforts should be made to reduce the impact of these factors. For example, measures such as improving equipment standards, optimizing process conditions, and enhancing storage conditions can be taken to increase particle strength and uniformity, as well as to reduce moisture content and packaging temperature; these are all effective ways to prevent caking. However, a more effective anti-caking measure is to treat the fertilizer to prevent caking. Common anti-caking agents currently in use include inert powders, inorganic salts, surfactants, and non-surfactants. (1) Inert powder coating: Inert powders are the earliest type of anti-caking agent to be used in the world. By coating fertilizer particles with inert powders, these powders adhere to the surface of the particles, thereby reducing caking. The powders used are mainly inert substances that are insoluble in water and do not undergo any chemical reactions with fertilizers; these typically include fine powders such as diatomaceous earth, kaolin, talc, and chalk ； These powders can also be used after treatment with fatty amines. Their function is to prevent fertilizers from absorbing moisture and to keep adjacent particles at a certain distance apart. The usage range is 1% to 4% (by weight). This method is cost-effective, but its drawback is that it is generally ineffective for highly decomposed fertilizers prone to caking; it also increases the dust content in the fertilizer and reduces its effective concentration. (2) Inorganic salts: Some inorganic salts that can be partially or fully hydrated possess anti-caking properties. These salts can combine with the moisture in fertilizers, thereby suppressing the dissolution of the fertilizers and capillary adsorption caused by water. Such anti-caking agents are particularly suitable for crystalline fertilizers. Magnesium nitrate, for example, can effectively prevent the caking of *ao acid an or sulfuric acid an. (3) Surfactants Surfactants are the most widely used anti-caking agents at present, possessing a special amphiphilic structure – hydrophilic polar groups and hydrophobic non-polar groups. It can change the surface tension between solids and liquids. Its mechanisms are generally believed to include preventing moisture, dispersing the liquid film, altering crystals, inhibiting dissolution and recrystallization, reducing adhesion between particles, and weakening the liquid film. After surfactants are adsorbed on the surface of particles, one end of their polar groups faces the crystal, while the non-polar end faces outward, forming a thin hydrophobic film on the particle surface. This film prevents water absorption and protects the crystalline water, thereby hindering moisture exchange between the particle product and the atmosphere. As a result, the dissolution and recrystallization processes on the particle surface are suppressed, reducing and eliminating caking in the product. Additionally, this hydrophobic film covering the surface of the particles also serves to mechanically isolate them from one another. Some of these are water-soluble surfactants, whose components reduce surface tension, allowing a film to form on the surface of the salt solution; this prevents crystal growth and reduces the tendency to caking. In fertilizers treated with surfactants, as moisture absorption leads to deliquescence, the surfactants adsorbed on the surface of the fertilizer particles dissolve in the absorbed water and remain at the fertilizer-water interface. It can be inferred that the presence of surfactants blocks the pathways for salt diffusion; their hydrophilic ends face the components with higher water absorption, preventing them from diffusing to the particle surface and contact areas, and also making it difficult for new crystals to form clumps. It exhibits excellent anti-caking effects even at low surfactant concentrations, that is, when only small amounts are used. Surfactants are divided into cationic, anionic, non-ionic, and amphoteric types. When carrying out anti-caking treatment for fertilizers, there is a high degree of selectivity regarding the type of fertilizer. Experiments show that anionic surfactants such as sulfonates and non-ionic surfactants such as polyethylene do not provide very good anti-caking effects for *AO acid AN, whereas fatty amines with long carbon chains exhibit strong anti-caking effects on *AO acid AN. Therefore, specifically, under what conditions which surfactant should be added to that type of fertilizer must be determined through experiments. In fact, an anti-caking agent has multiple functions. The polymer surfactant complexes formed by dissolving water-soluble or water-insoluble polymers in concentrated surfactant solutions exhibit a significantly greater synergistic effect compared to the use of each component alone. Solutions of polyvinyl acetate dissolved in sodium alkylbenzene sulfonate show a notable anti-caking effect when used to treat urea, and polyvinyl alcohol and its acetal derivatives, as well as polyacrylates, are all effective in this regard. Fertilizers treated with polymer surfactants form many needle-like crystals upon drying; they do not tend to clump even when the relative humidity of the air is higher than the fertilizer’s critical relative humidity, and they require a small amount to be effective. It can be inferred that this is mainly the result of changes in crystallinity*. (4) Non- surfactants Non-surfactants are mainly organic hydrophobics, such as paraffin, synthetic polymers, mineral oils, etc. Although they do not possess surfactant properties, they can form a waterproof layer on the surface of fertilizer particles, preventing those particles from absorbing more water and thus stopping caking that occurs due to capillary absorption. This method works well when the ambient temperature is not too high, but its effectiveness drops rapidly at higher temperatures. Since the hydrophobic layer cannot completely prevent fertilizer particles from absorbing moisture, high temperatures can lead to its breakdown; once this occurs, it results in severe caking. 4. Anti-caking treatment technology: Recent research on anti-caking technologies has shown that while the use of surfactants as anti-caking agents can reduce the hygroscopicity of materials, their mechanical isolation effect is weak, and they cannot prevent the formation of connections between crystal grains over a long period of time. Therefore, the current approach in developing anti-caking agents for fertilizers is to combine surfactants with other substances such as inert powders and polymer compounds, in order to improve the performance of these anti-caking agents. By combining surfactants with inert inorganic additives and ensuring their uniform dispersion on the particle surface to prevent the bonding of grains, a better anti-caking effect can be achieved. The combined use of surfactants such as alkylbenzenesulfonates, alkylsulfates, and alkylnaphthenesulfonates, along with materials like bentonite and kaolin, proves effective in preventing caking in compound fertilizers. Using polymer-surfactant adducts, which are polymers dissolved in concentrated surfactant solutions due to water-soluble or water-insoluble polymers, as anti-caking agents yields a significant synergistic effect compared to using either component alone. Polyvinyl acetate solutions solubilized with sodium dodecylbenzenesulfonate, when used directly or after dilution, to treat urea, ammonium sulfide, and ammonium chloride, exhibit a significant anti-caking effect. Representative polymer compounds include polyvinyl alcohol and certain acetal compounds, polyacrylates, polyvinyl alkyl ethers, and polyacrylamides, etc ； Representative surfactants include sodium dodecyl sulfate, sodium oleate, sodium alkyl naphthenesulfonate, and alkyl (aryl) polyoxyethylene ethers, etc. Alkyl sulfate formula products are suitable for encapsulating urea products. Hydrogenated lipid alkyl amines are considered the most widely used oil-soluble organic anticaking agents. Fatty amine products are particularly suitable for ** and **-based fertilizers. This is due to the exchange of ammonium ions and their binding with fatty amine ions in the crystal structure ； They can also be used as crystallization modifiers to treat products with more complex structures. Polyoxyethylene condensate is the most common non-ionic surfactant, which can be used as a component in anti-caking agents for compound fertilizers. In addition, there are hydrophobic non-ionic anticaking agents such as paraffin, synthetic polymers, and mineral oils. Solid encapsulants are applied to hot fertilizer after being melted into solids, particles, or tablets. The earliest formula product was a fatty amine dissolved in mineral oil. A recent development has been the addition of hydrophobic surfactants, such as paraffins and polyethylene components, to further improve moisture resistance and reduce dust. However, such components should not penetrate too deep into the particles, as this will reduce their dust-proofing ability and affect their long-term anti-caking performance. The solid encapsulant must be melted and applied to the surface of the fertilizer particles before the temperature of the fertilizer drops to the melting point of the encapsulant. Solid formulation encapsulants are currently mainly used for potassium chloride and low-density **. The combined use of inert powder and liquid encapsulants allows the addition amount to be reduced to 0.1%–0.3%, resulting in dust-free fertilizers. It is economical to use inert powdery coatings for fertilizers that tend to clump. The commonly used surfactants for preventing fertilizer caking and the corresponding treatment methods are shown in Table 2. Common methods for preventing caking of chemical fertilizers are shown in Table 3. With the advancement of production technologies for compound fertilizers and the increasing demands from users regarding their quality, anti-caking treatment of compound fertilizers has become an essential step in their production process. The general method of use involves adding a powder spraying cylinder behind the finished product sieve; the finished particles are fed into this cylinder, where the powder or oil-based anti-caking agent is sprayed onto their surface as they roll. The particles must also roll at a certain speed within the drum, so that the coating on their surface can have sufficient strength. 5. Conclusion: The climate in the south is warm and humid, which makes it easy for fertilizers to clump together. In the north, compound fertilizers stored for use in winter also tend to clump over time due to their long storage period. Therefore, preventing fertilizer caking is an important measure to improve product quality and enhance product competitiveness. As domestic compound fertilizer manufacturers have become more aware of the importance of product quality, this has strongly promoted research and application of anti-caking agents for fertilizers in China, leading to the emergence of many specialized manufacturers of such agents. However, there are a wide variety of fertilizer anti-caking agents, with different treatment methods and processes that yield varying results. Moreover, the process technologies and production conditions vary greatly among different compound fertilizer manufacturers; it is advisable to conduct batch tests before use, and to apply the agent only after confirming its effectiveness, in order to achieve the best anti-caking results. 【Author Introduction】 Chen Mingliang: Deputy Director, Senior Engineer. He graduated with a master’s degree in 1986 and began working at the Shanghai Institute of Chemical Technology, where he has been engaged in research and development related to fertilizer processes and engineering for many years. As the project leader, I have taken charge of **two key projects, published multiple papers, and filed several invention patents. Table 2: Surfactants for Preventing Fertilizer Caking and Treatment Methods
Surfactant | Treatment Method | Types of Fertilizers Suitable for Use
1) Anionic surfactants such as alkyl sulfates, alkyl benzene sulfonates, and alkyl naphthalene sulfonates | Surface treatment of particles | Ammonium sulfate, **
2) The aforementioned anionic surfactants combined with bentonite or kaolin, along with fatty acids and their derivatives sowie alkyl amine salts | Surface treatment of particles | Urea, compound fertilizers
3) Anionic surfactants such as alkyl benzene sulfonates, secondary alkyl sulfates, and pentadecyl sulfonyl chloride, as well as diaminodicyano compounds of the amphoteric type | Surface treatment of particles or participation in the crystallization process | Ammonium bicarbonate
4) Heptadecyl to eicosyl amines | Surface treatment of particles | Ammonium chloride
5) Polymer-surfactant complexes, fatty amine mineral oil agents. Among them, polymers include polyvinyl acetate, polyvinyl butyral, polyacrylate, polyvinyl alcohol and some of its acetals, polyvinyl alkyl ethers, and polyvinyl acrylamide. Surfactants include alkyl sulfates, alkylbenzenesulfonates (naphthenesulfonates), and alkyl polyoxyethylene ethers. For particle surface treatment or participation in the crystallization process: ammonium phosphate, superphosphate, urea, heavy calcium carbonate, phosphoric acid fertilizers, ammonium sulfate, ammonium chloride. 6) Amine salts, either in their cationic form or in combination with inert agents, for particle surface treatment; compound fertilizers. Table 3: Common chemical fertilizer anti-caking methods. Evaluation of anti-caking agents: Non-water-soluble powder method (suitable for particle surfaces): kaolin, diatomite, talc, clay, china clay, silica powder, mica powder, bentonite, activated clay, alumina, magnesium oxide (slag powder), silica, sulfur, calcium carbonate, magnesium carbonate, calcium silicate, etc. 1) Not limited by the type of fertilizer. 2) Little effect if used in low quantities. 3) The anti-caking effect does not last long. Waterproof film-forming method (suitable for particle surfaces): waxes, resins, asphalt, machine oil, polyvinyl alcohol and other film-forming substances. 1) Significant anti-caking effect. 2) Difficult to apply and high cost. Surfactant method: surfactants or their combinations with polymers and inorganic salts, acidic aniline dyes, etc. 1) Very effective anti-caking effect. 2) Good selectivity between the fertilizer and the anti-caking agent. 3) Suitable for both particle surfaces and can be added during the production process

Generally, the methods mentioned above can effectively alleviate clumping, but these fertilizers are prone to clumping in the first place, and they will definitely clump to some extent.

A good anti-caking method has been found, thank you!

Please note that oil-based anti-caking agents cannot be used in top-dressing fertilizers, as this makes the raw materials used in such formulations less appropriate! Consider the issue of ingredients and dehumidification in the processing environment!

Has the original poster found any good methods??? Please share them...... Clumping is more severe with liquid fertilizers than with compound fertilizers... Ordinary powdered anti-caking agents don’t work very well either... The oil spraying method is even less feasible... One can choose powdered anti-caking agents that contain water-absorbing and retention agents... I suggest adding some organic substances to the formula as well; for example, sodium humate... It prevents clumping and also provides organic matter... Hehe

The article from the Shanghai Chemical Industry Institute on caking and anti-caking in compound fertilizers is really detailed,,,,,, I learned a lot from it；

The dehumidification device performs well from July to September, especially regarding nitrates. . . .

For top-dressing fertilizers, it is recommended to try adding a certain proportion of silica to see the effect.

Generally, topdressing fertilizers are required to have good solubility, and the use of oily anti-caking agents may have an impact.