organic fertilizer production line

Introduction: A Model of Cross-Disciplinary Innovation in the Circular Economy

Amid the global wave of energy transition, the popularity of electric vehicles has brought about an increasingly severe challenge—the fate of a large number of retired lithium iron phosphate (LFP) power batteries. Traditional hydrometallurgical recycling primarily focuses on extracting lithium, which is economically suboptimal and fails to fully utilize the phosphorus resource that constitutes nearly 40% of the battery’s mass. Simultaneously, modern agriculture faces the dual challenges of acidic soil remediation and low phosphorus fertilizer efficiency. A groundbreaking technology ingeniously connects these two seemingly unrelated problems. Through innovative chemical processes, it directly converts retired LFP batteries into a slow-release phosphorus fertilizer that performs exceptionally well in acidic soils. This is not only a major innovation in the field of resource recovery but also opens a new path for nutrient supply in green agriculture, serving as a vivid practice of the circular economy concept at the intersection of new energy and agriculture.

I. Core Technology: A Four-Step Transformation from Battery to Fertilizer

This technology follows a clear, efficient, and environmentally friendly process route, divided into four key steps that achieve the precise conversion from waste electrode materials to functional fertilizer.

Step 1: Mild and Efficient Electrode Delamination

The process begins with separating the battery cathode active material from the aluminum foil current collector. Unlike traditional strong acid stripping or high-temperature incineration, this technology employs a mild chemical stripping solution assisted by ultrasonic treatment. The cavitation effect generated by ultrasound efficiently breaks the adhesion of the binder (e.g., PVDF) while avoiding harsh reactions that could damage the crystal structure of the active material. This step yields uniform, high-purity lithium iron phosphate (LiFePO₄) black powder, laying the foundation for subsequent selective extraction.

Step 2: Selective Lithium Extraction and Retention of Phosphorus-Iron Solid Phase

This is the key to the economic viability of the entire process. Using mild oxidants such as sodium persulfate (Na₂S₂O₈) under specific conditions, lithium ions (Li⁺) in LiFePO₄ are selectively oxidized and leached into the solution, while iron (Fe) and phosphorus (P) elements are retained in the solid phase as insoluble iron phosphate (FePO₄). This method achieves efficient, high-purity lithium recovery (which can be subsequently converted into lithium carbonate products) while ensuring that phosphorus and iron resources are not lost. This precise separation creates the conditions for the targeted utilization of phosphorus.

Step 3: Efficient Phosphorus Release and Resource Conversion

The solid phase after delithiation is mainly FePO₄, from which phosphorus needs to be released and converted into a plant-available form. Through reaction with reagents such as sodium sulfide (Na₂S), phosphorus is efficiently transferred into an aqueous solution in the form of specific ions (e.g., dihydrogen phosphate, H₂PO₄⁻). The phosphorus recovery rate in this step is extremely high, exceeding 99.5% under laboratory conditions, ensuring maximum resource utilization. It is worth noting that the by-products of this reaction (e.g., iron sulfide) also have potential value as photocatalytic materials, further embodying the zero-waste concept of “utilizing everything to the fullest.”

Step 4: Synthesis of Acid-Resistant Slow-Release Phosphorus Fertilizer

This is the functional core of the technology. The obtained phosphorus-containing solution (containing precisely controlled molar ratios of hydrogen phosphate, HPO₄²⁻, and dihydrogen phosphate, H₂PO₄⁻) is used as a functional monomer and mixed with raw materials such as acrylic acid and urea. In the presence of an initiator and under nitrogen protection, free radical polymerization is carried out at 50-80°C. The key to this reaction is that phosphate ions act as cross-linking agents and stabilizers, forming a dense hydrogen bond network with the carboxyl groups on the polyacrylic acid chains and creating an interpenetrating structure with urea, ultimately building a stable three-dimensional polymer hydrogel network. The fertilizer nutrient (phosphorus) is chemically bonded or physically encapsulated within this network.

II. Core Advantages: Triple Breakthroughs in Economics, Performance, and Environmental Protection

The disruptive potential of this technology stems from its significant advantages across multiple dimensions.

• Disruptive Economic Model:Traditional LFP battery recycling suffers from poor economics due to the lack of high-value cobalt and nickel. This technology adopts a “lithium + phosphorus” dual-recovery model, converting the phosphorus that constitutes the bulk of the battery mass into high-value-added agricultural products. Calculations estimate that introducing this technology can yield a net profit of approximately $2,035 per ton of retired batteries processed, completely reversing the “unprofitable” situation of LFP recycling and providing strong commercial drivers for the recycling industry.
• Outstanding Acid-Resistant Slow-Release Performance:Traditional polymer slow-release fertilizers tend to have their network structure collapse due to protonation in acidic soils, leading to nutrient “burst release” or failure. In the fertilizer synthesized by this technology, phosphate groups play a dual role: first, as strong hydrophilic groups and cross-linking points, they enhance the stability and water retention of the network in acidic environments; second, they possess pH buffering capacity, partially neutralizing soil acidity and providing an ideal microenvironment for steady, long-lasting nutrient release. This makes it particularly suitable for the vast areas of acidic red and yellow soils in southern China.
• Green and Environmentally Friendly Throughout the Process:The entire process avoids the use of strong acids, strong alkalis, or high-temperature calcination. The reagents are mild, and by-products can be resource-utilized, basically generating no difficult-to-treat secondary pollution. The transformation from electronic waste to an environmentally friendly fertilizer achieves true clean production and a closed resource loop.

III. Application Prospects and Future Directions

The successful development of this technology holds broad application value and profound social significance.

In Agriculture: It provides an innovative product to address the worldwide challenges of severe phosphorus fixation in acidic soils and low fertilizer efficiency. Preliminary experiments indicate that this fertilizer can effectively promote the growth of crops like corn. It can achieve the same or even higher yields while reducing phosphorus fertilizer application by 30%-50%, significantly lowering the risk of phosphorus loss through runoff. This has a positive effect on protecting water bodies and preventing eutrophication.

In Resource Circulation: It points the way for the high-value, resource-based utilization of millions of tons of retired LFP batteries annually. It is a key technological node in constructing the grand cycle of “battery production – use – recycling – material regeneration – agricultural feedback,” strongly supporting the sustainable development of the new energy vehicle industry.

Future Development Focus: Current research is primarily at the laboratory stage. Future work will focus on: 1) Process Engineering Scale-up: Optimizing continuous production processes, reducing equipment and operational costs, and promoting the industrialization of the technology; 2) Systematic Agricultural Validation: Conducting large-scale, long-term field trials on various types of acidic soils and multiple crops to comprehensively evaluate its agronomic effects and environmental benefits; 3) Product Series Development: Building on the existing phosphorus fertilizer, introducing potassium, calcium, magnesium, and trace elements to develop specialized compound slow-release fertilizers for different scenarios such as dryland farming, protected horticulture, and economic forests; 4) Technology Extension Applications: Exploring the application of this technological concept to the resource treatment of other phosphorus-containing wastes (e.g., phosphorus-rich sludge, phosphogypsum), expanding its application boundaries.

Converting discarded lithium iron phosphate batteries into acid-resistant, slow-release phosphorus fertilizer is a cutting-edge technology that integrates materials science, environmental engineering, and agronomy. It cleverly solves the dual challenges of “difficult disposal of waste batteries” and “difficult fertilization of acidic soils,” achieving a transformative “waste-to-resource” solution. This technology not only demonstrates the immense potential of interdisciplinary resource recycling but also provides a highly promising technological blueprint for the green transformation of global agriculture and the closed-loop development of the new energy industry. As the technology matures and is widely adopted, we have reason to believe that these batteries, which once powered electric vehicles and traveled thousands of miles, will continue to nourish the earth in another form after their retirement, sustaining life for generations to come.

A Circular Blueprint: From Batteries to Farmland

The conversion of spent lithium iron phosphate batteries into acid-resistant, slow-release phosphorus fertilizer represents a paradigm shift in resource recovery. This interdisciplinary innovation addresses both critical waste management and sustainable agriculture challenges, creating a truly circular “waste-to-resource” pathway with significant environmental and economic potential.

To scale this transformative process, the recovered nutrient materials can be integrated into conventional fertilizer granulation processes. The phosphorus-rich compound can be blended into formulations using an npk blending machine and then shaped into uniform granules via advanced granulation technology. Depending on the desired product characteristics, a disc granulator (as part of a disc granulation production line) or a double roller press granulator can be employed within a complete npk fertilizer production line. This integration with professional fertilizer manufacturing equipment ensures the final product meets agronomic standards for efficient, controlled-release application.

Ultimately, this technology exemplifies a powerful synergy between the new energy and agriculture sectors. It promises a future where batteries, after powering our vehicles, can be reborn as vital nutrients that nourish crops and regenerate soils, closing the loop in a truly sustainable economy.

 Introduction: From Extensive Application to Intelligent Supply

Nitrogen is a key element for crop growth, but the global average utilization rate of traditional nitrogen fertilizers is only 30%-50%. A large proportion of unused nitrogen is lost through ammonia volatilization, nitrate leaching, or greenhouse gas emissions, causing significant resource waste and severe environmental pollution. The core solution to this problem lies in achieving precise spatiotemporal matching between nitrogen supply and crop demand. Smart/stabilized fertilizers, centered on intelligent nitrogen regulation and adsorption technologies, are leading a profound agricultural technology revolution. They are no longer simple nutrient carriers but integrated “intelligent nutrient management systems” incorporating multidisciplinary wisdom from materials science, information sensing, and microbiology. Their aim is to maximize fertilizer benefits while minimizing environmental footprints, providing key technological support for the green and sustainable development of agriculture.

I. Intelligent Nitrogen Regulation: Making Fertilizers “Think”

The goal of intelligent regulation technology is to achieve on-demand, timely, and precise release of nitrogen, with its core lying in “sensing” and “responding” to environmental or biological signals.

1. Responsive Slow-Release Regulation: This is an outstanding application of materials science. By designing ingenious coating or carrier materials, fertilizers can be made to “understand” the “language” of crops. For example, urea encapsulated in nanoparticles made of polylactic-co-glycolic acid has a degradation rate regulated by the concentration of specific organic acids (like citric acid) secreted by roots. When root growth is active and nitrogen demand is high, increased citric acid secretion triggers accelerated degradation of the capsule wall, precisely releasing nitrogen. Field trials on corn show this technology can increase the synchronization rate between the nitrogen release curve and the root absorption peak to 92%. Similarly, pH-sensitive hydrogel coating materials can sense micro-changes in rhizosphere pH caused by crop ion uptake and automatically disintegrate when the pH drops to a specific threshold, making them particularly suitable for crops like rapeseed that strongly secrete H⁺ from their roots.

2. Intelligent Monitoring and Regulation: This represents the integration of digital agriculture and precision fertilization. By deploying IoT devices such as optical sensors and soil solution samplers in fields, real-time monitoring of soil nitrogen dynamics and crop nitrogen nutritional status is achieved. This data is fed into models for soil nitrogen transport and crop nutrient diagnosis, forming prediction and early warning systems. Ultimately, an intelligent decision-making system drives fertigation equipment to implement “prescription-based” variable rate fertilization. Trials in Tianjin showed that this technology system reduced nitrogen fertilizer input by over 30% while maintaining vegetable yields, achieving synergy between water/fertilizer saving and yield increase.

3. Microbial Regulation: This method utilizes natural forces for intelligent regulation. It involves inoculating beneficial microorganisms, such as arbuscular mycorrhizal fungi, to establish a symbiotic relationship with crop roots. Their vast hyphal network acts like an “internet” within the soil, greatly expanding the root system’s absorption range. The glomalin-related proteins secreted by the hyphae not only stabilize soil aggregates but also strongly adsorb ammonium nitrogen, significantly reducing gaseous nitrogen loss (by up to 48%), and slowly transferring the captured nitrogen to the host plant, thereby achieving efficient and stable biological nitrogen fixation and supply.

II. Nitrogen Adsorption Technology: Adding a “Safety Lock” to Leaching Nitrogen

While regulating release, how to “lock in” nitrogen that has been released but not yet timely absorbed by roots to prevent its loss is another critical technological challenge. Adsorption technology provides a solution.

Modified Carbon Materials as the Main Force: Materials like activated carbon and biochar possess enormous specific surface areas and rich pore structures, making them naturally excellent adsorbents. Impregnation modification with chemicals like boric acid and potassium sulfate can further enhance their targeted adsorption capacity for ammonia or nitrate. For instance, using modified activated carbon compounded with diatomaceous earth to create a fertilizer coating can convert volatilized ammonia in situ into more stable ammonium nitrogen, reducing losses to the atmosphere. Mixing modified biochar with bentonite to create a deep-layer barrier material placed in the soil profile can efficiently intercept nitrate leaching with water, with an adsorption capacity of up to 35 mg/g, minimizing the risk of deep leaching.

Composite Matrices Constructing Synergistic Defenses: Single materials have limited performance; compositing is the trend. Scientifically combining materials such as biochar, humic acid, diatomaceous earth, and activated clay can construct functionally complementary “sponge plow layers” or fertilizer coatings. This structure can not only physically adsorb and chemically bind various forms of nitrogen but also improve soil structure and enhance overall water and nutrient retention capacity, achieving a win-win for “loss control” and “soil improvement.”

III. Synergistic Application: The Birth of Smart/Stabilized Fertilizers

Intelligent regulation and adsorption technologies do not exist in isolation; their organic combination has given rise to a new generation of smart/controlled-release fertilizers. For example, a 16-16-16 compound fertilizer might use fast-acting nutrients as its core, first coated with a layer of modified biochar to adsorb prematurely released nitrogen, and then covered with a pH-responsive smart coating to control nutrient release time. Another design involves directly embedding microbial agents (e.g., plant growth-promoting rhizobacteria) compounded with biochar into the fertilizer granules, simultaneously exerting biological regulatory effects to enhance nutrient absorption and preventing nutrient loss through physical adsorption.

Field application data demonstrates their superior performance: compared to traditional fertilizers, these smart fertilizers can reduce nitrogen leaching by 56.9%-78.7%, reduce ammonia volatilization by more than 35%, and increase nitrogen fertilizer utilization efficiency by more than 20 percentage points. These fertilizer granules also possess better physical strength (e.g., compressive strength reaching 3.8 MPa), facilitating mechanical application and storage.

Conclusion: The Era of Intelligent Fertilizer Design

The advancement of intelligent nitrogen regulation and adsorption technologies signifies a transformative shift in fertilizer science—from conventional formulation to precision intelligent design. These innovations transform fertilizers from passive nutrient carriers into active management systems that respond dynamically to crop needs and environmental conditions.

This evolution is fundamentally reshaping the npk fertilizer manufacturing process. Modern npk fertilizer production line systems now integrate intelligent materials with advanced fertilizer granulation equipment. Key technologies like the fertilizer roller press machine and npk granulation machine technology enable precise control over nutrient release profiles within the manufacturing of npk fertilizer.

Such innovations in npk fertilizer production technology support both agricultural efficiency and environmental sustainability. As these technologies mature through integration with materials science and biotechnology, they will drive the development of smarter, more responsive npk fertilizer machine equipment, contributing significantly to sustainable agriculture and ecological balance.

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Functional/specialty fertilizers are a category of fertilizers that combine nutrient supply with specific physiological functions. Their core is based on macro- and micro-elements like nitrogen, phosphorus, and potassium, with the addition of functional components such as humic acid, seaweed extract, biochar, and silicon, or modified using special processes like magnetization and activation. This achieves the dual goals of “fertilization + solving specific production problems,” meeting the needs of modern agriculture for enhancing crop resistance, improving soil quality, and optimizing agricultural product quality.

Core Categories and Mechanisms of Action

The function of functional/specialty fertilizers is strongly correlated with their added core components. Different categories address different production pain points. Common types include:

Humic Acid-Containing Fertilizers

Core Components: Humic acid (mainly fulvic acid and brown humic acid) extracted from peat, lignite, and weathered coal.

Dual Functions

Nutrient Supply: Can be combined with nitrogen, phosphorus, and potassium to create humic acid compound fertilizer, providing essential nutrients for crop growth.

Soil Improvement + Growth Stimulation: The functional groups of humic acid can adsorb heavy metal ions in the soil, reducing the risk of soil pollution; it also promotes the formation of soil aggregates, improving soil permeability and water and fertilizer retention capacity; and it stimulates root cell division, enhancing root absorption capacity and strengthening crop drought and cold resistance.

Applicable Scenarios: Improvement of saline-alkali land and compacted soil; base fertilizer or top dressing for field crops and fruit trees.

Contains Alginic Acid Fertilizer

Core Ingredients: Natural bioactive substances (algal polysaccharides, amino acids, cytokinins, etc.) extracted from seaweed such as kelp and algae. Dual Functions

Nutrient Supply: Seaweed itself contains nitrogen, phosphorus, potassium, and trace elements such as zinc and boron, which can directly supplement crops with nutrients.

Stress Resistance and Yield Promotion + Quality Improvement: The bioactive substances in alginic acid can activate the crop’s own defense system, enhancing resistance to pests and diseases, lodging resistance; promoting fruit enlargement and coloring, increasing fruit sugar and vitamin content, and improving the flavor of agricultural products.

Applicable Scenarios: Foliar spraying or fertigation for cash crops such as fruits, vegetables, and flowers; restorative fertilization during periods of crop stress (drought, low temperature).

Silicon Fertilizer

Core Components: Soluble silicon compounds such as monosilicic acid, potassium silicate, and calcium silicate (distinct from the insoluble silicon in traditional silicon ores).

Dual Functions

Nutrient Supply: Silicon is a “beneficial element” for crops (especially important for silicon-loving crops like rice, wheat, and sugarcane), participating in cell wall synthesis;

Stress and Disease Resistance + Lodging Resistance: Silicon deposits in crop epidermal cells, forming hard “silicified cells,” enhancing stem toughness and reducing the risk of lodging; it also blocks pathogen invasion, reducing the occurrence of diseases such as rice blast and wheat powdery mildew; and it can reduce fruit deformities and cracking rates in fruits and vegetables.

Applicable Scenarios: Rice, wheat, corn, and other gramineous crops; cucumbers, tomatoes, and other greenhouse vegetables.

Biochar-Based Fertilizer

Core Components: Biochar, produced by high-temperature pyrolysis of biomass (straw, sawdust, livestock manure, etc.) under anaerobic conditions, combined with organic or chemical fertilizers.

Dual Functions

Nutrient Supply: Biochar’s pores adsorb and fix nutrients such as nitrogen, phosphorus, and potassium, slowly releasing them for crop absorption.

Carbon Fixation and Soil Improvement + Fertilizer Retention and Efficiency Enhancement: Biochar’s porous structure improves soil permeability, adsorbs soil salts, and alleviates secondary salinization in greenhouse agriculture soils; it also fixes atmospheric carbon, achieving “carbon sequestration and emission reduction”; and promotes the reproduction of beneficial soil microorganisms, improving soil fertility.

Applicable Scenarios: Soil improvement in greenhouses; fertility enhancement in barren and sandy soils.

Magnetized Fertilizer

Core Technology: Ordinary fertilizers (urea, compound fertilizer) are magnetized using a magnetization device.

Dual Functions

Nutrient Supply: Retains the original fertilizer’s nutrient content, meeting the basic needs of crops.

Nutrient Activation + Enhanced Absorption: The magnetic field alters the form of nutrients in the soil, converting insoluble phosphorus and potassium into soluble forms; it also stimulates root enzyme activity, accelerating nutrient absorption and improving fertilizer utilization.

Applicable Scenarios: Base fertilizer for field crops; areas with severe soil nutrient fixation.

Core Advantages

Multiple Effects in One Application, Solving Specific Production Pain Points

Unlike ordinary fertilizers that only provide nutrients, functional fertilizers can simultaneously achieve “nutrient supplementation + soil improvement + stress resistance + quality improvement and yield increase.” For example, humic acid compound fertilizer can both fertilize and improve compacted soil, saving the cost of applying soil conditioners separately.

Enhancing Crop Stress Resistance and Reducing Pesticide Use

Silicon fertilizers, seaweed extract fertilizers, etc., can enhance the crop’s own disease and stress resistance, reduce the incidence of pests and diseases, and reduce the use of chemical pesticides, aligning with the development direction of green agriculture.

Adapting to Precision Planting Needs

Customized functions for different crops and different soil problems. For example, biochar-based fertilizers are used in greenhouses to improve saline-alkali soils, and seaweed extract fertilizers are used in fruit and vegetable cultivation to improve fruit quality, meeting the differentiated planting needs of modern agriculture.

III. Precautions for Use

Targeted Selection, Avoid Blind Application

Fertilizers should be selected based on soil conditions and crop needs. For example, humic acid fertilizers are preferred for saline-alkali soils, while silicon fertilizers are preferred for paddy fields. Do not blindly pursue “multi-functionality” while neglecting targeted application.

Use in conjunction with conventional fertilizers

Most functional fertilizers have lower levels of macronutrients than ordinary compound fertilizers and must be used in conjunction with conventional fertilizers to meet the nutrient needs of crops throughout their entire growth cycle.

Strictly control the application dosage

Excessive application of some functional ingredients (such as humic acid) can lead to soil microbial imbalance. Follow the dosage instructions on the product packaging to avoid adverse effects.

Conclusion: Integrating Functional Fertilizers into Modern Agriculture

In summary, functional/specialty fertilizers represent a significant advancement in agricultural inputs, moving beyond mere nutrient supply to address specific challenges like soil degradation, crop stress, and quality optimization. Their targeted application—whether humic acid for saline soils or silicon for gramineous crops—enables precise, sustainable crop management.

To fully leverage these advanced formulations, professional fertilizer production machine technology is essential. For instance, a versatile NPK fertilizer production line can be adapted to incorporate functional additives. Critical equipment includes:

• Disc granulatorsor double roller press granulators for shaping uniform, high-integrity granules that encapsulate both macro-elements and functional components.
• NPK blending machinesfor homogeneously mixing base nutrients with additives like biochar or seaweed extract.
• Specialized lines, such as a bio organic fertilizer production linefor humic-acid or biochar-based products, often integrated with windrow composting machines for pre-treatment of organic matter.

Choosing the correct fertilizer granulation processes ensures product stability and efficacy. A roller press granulator production line is ideal for moisture-sensitive materials, while a disc granulator for shaping offers flexibility for organic-inorganic blends.

Ultimately, the synergy between innovative functional fertilizers and professional fertilizer manufacturing equipment paves the way for more resilient, efficient, and sustainable farming systems. By selecting the right fertilizer type and employing precise manufacturing technology, producers can deliver solutions that truly meet the dual goals of nourishment and problem-solving in modern agriculture.

Sulfur-coated urea (SCU) is a matrix-based composite controlled-release fertilizer. Its core feature is a thin film of sulfur coated on the surface of urea granules. Some products also have an additional wax or resin sealing layer. By controlling the decomposition rate of the coating, nitrogen release is slowed down, while simultaneously supplementing crops with essential sulfur. It possesses the dual functions of “nitrogen control and sulfur supply,” making it a commonly used low-cost slow-release fertilizer for field crops and cash crops.

I. Core Preparation Process

The core of sulfur-coated urea production is precise coating spraying technology. Strict control of temperature and spraying rate is required to ensure uniform coating thickness. The specific process is as follows:

Urea Pretreatment:Urea granules with uniform particle size are preheated to a specific temperature to enhance the adhesion between the granules and molten sulfur.

Molten Spraying:Sulfur is heated to a molten state and evenly sprayed onto the surface of the preheated urea granules in a rotating drum. Depending on the product’s release cycle requirements, an additional layer of wax or resin can be sprayed as a sealing layer to improve coating stability.

Cooling and Shaping: After spraying, the granules cool and solidify, forming a two- or three-layer structure of “urea core + sulfur coating (optional wax/resin sealing layer)”.

Thickness Control: The coating thickness is controlled by adjusting the sulfur melting temperature, spraying rate, and roller speed—a thin coating corresponds to rapid release (suitable for short-term growing crops), while a thick coating corresponds to long-term release (suitable for perennial crops or field basal fertilizer).

II. Nutrient Release Mechanism: The release of nitrogen and sulfur from sulfur-coated urea relies on the natural decomposition process in the soil environment. The release process is highly compatible with the crop’s nutrient requirements and consists of two simultaneous stages:

Coating Decomposition Stage: Water vapor in the soil permeates the coating, while soil microorganisms (such as sulfur-oxidizing bacteria) gradually decompose the sulfur coating. If a wax/resin sealing layer is present, it will first break down under microbial or physical action, initiating the decomposition of the sulfur layer.

Nutrient Release Stages

Nitrogen Release: As the coating develops pores, soil moisture enters the granules, dissolving the urea. Nitrogen slowly diffuses into the soil through these pores, with a release cycle controllable within 8-12 weeks, avoiding the problem of “one-time release and massive loss” common with ordinary urea.

Sulfur Release: Decomposed sulfur is converted into sulfate, which is absorbed and utilized by crops. Sulfur is a key medium-element for protein synthesis and enzyme activity activation, promoting crop metabolism and improving the quality of agricultural products.

III. Core Advantages

Extended Nitrogen Supply Cycle, Improved Utilization Rate

Ordinary urea releases a large amount of nitrogen within 1-2 weeks after application, with a utilization rate of only 30%-40%. Sulfur-coated urea releases nitrogen slowly, increasing the utilization rate to over 50%, reducing nitrogen loss due to leaching and volatilization, and continuously supplying the crop’s needs throughout its entire growth period.

Dual-purpose fertilizer, supplementing sulfur

Unlike polymer-coated controlled-release fertilizers, sulfur-coated urea’s coating itself is a sulfur source, effectively addressing sulfur deficiency-related issues such as leaf yellowing and weakened growth in crops. It is particularly suitable for sulfur-deficient soils (such as sandy soils and fields where sulfur-required crops are grown long-term).

Reduced fertilization costs, saving labor and time

The long-lasting nitrogen release allows for single-application as base fertilizer, eliminating the need for multiple topdressings. This significantly reduces labor and fuel inputs, meeting the needs of large-scale mechanized planting of field crops such as wheat, corn, and cotton.

Environmentally friendly, meeting regulatory requirements

The slow-release nitrogen minimizes farmland runoff pollution and ammonia volatilization, reducing the impact on eutrophication of water bodies and the atmospheric environment, aligning with agricultural policies aimed at reducing fertilizer use and increasing efficiency.

IV. Production and Quality Control Key Points

Key control parameters: During production, precise control of the sulfur melting temperature (ensuring complete melting without decomposition), spray uniformity (avoiding excessively thick or thin coatings in certain areas), and cooling rate (preventing coating cracking) is crucial.

Customized Release Curves: By adjusting the coating thickness and sealing layer type, different nutrient release curves can be customized. For example, thin-coated products are suitable for topdressing crops, while thick-coated products are suitable for base fertilizer of perennial crops such as fruit trees and seedlings.

V. Precautions for Use

Impact of Soil Acidity: Long-term, large-scale application of sulfur-coated urea will lower the soil pH due to the decomposition of sulfates, leading to soil acidification. It is recommended to use it in acidic soils in conjunction with alkaline materials such as quicklime or wood ash, or to alternate it with alkaline fertilizers to maintain soil acid-base balance.

Application Method: Trench or hole application is required; avoid surface spreading—high temperature and drought on the surface will accelerate coating damage and impair the controlled-release effect. Also, do not crush it before use, otherwise the coating structure will be destroyed, and the controlled-release function will be lost.

Suitable Crops: Prioritized for field crops such as wheat, corn, and rice, as well as crops with high nitrogen requirements and sulfur needs such as fruit trees and lawns. Not suitable for aquatic crops (such as lotus root), as rapid decomposition of the coating will lead to nitrogen loss.

Conclusion: Integrating SCU into Modern Fertilizer Production Systems

In conclusion, sulfur-coated urea represents a significant advancement in controlled-release fertilizer technology, offering an economical solution for sustainable nutrient management. Its successful npk fertilizer manufacturing process can be integrated into broader npk fertilizer production lines to create specialized formulations. While SCU production primarily employs drum coating, other key technologies like the double roller press granulator are essential in modern npk fertilizer production technology. For NPK compound fertilizers, dry granulation processes using a fertilizer roller press machine offer an alternative for heat-sensitive materials, with the npk bulk blending machine enabling precise nutrient ratio customization.

The scalability of SCU production complements the high NPK compound fertilizer production capacity demanded by global agriculture. When evaluating the NPK fertilizer production price, the long-term agronomic benefits and reduced environmental impact of controlled-release products like SCU justify the investment. Ultimately, integrating SCU technology with npk fertilizer granulator machine equipment and npk granulation machine technology creates versatile production systems capable of manufacturing a spectrum of products—from specialized controlled-release fertilizers to blended NPK formulations—supporting efficient, precise, and sustainable agriculture worldwide.

Stabilized fertilizers are a type of modified fertilizer that regulates nutrient conversion processes by adding chemical inhibitors. The core principle is to incorporate urease inhibitors and/or nitrification inhibitors into ordinary fertilizers (mainly urea and nitrogen-containing compound fertilizers) to slow down the conversion rate of nitrogen in the soil, reducing nitrogen loss in the form of ammonia and nitrogen gas, thereby improving nitrogen fertilizer utilization. While both stabilized and controlled-release fertilizers are high-efficiency nitrogen fertilizers, their technical principles and application scenarios differ significantly.

I. Core Technical Principle: Mechanism of Action of Inhibitors

The core of stabilized fertilizers lies in the synergistic or individual action of two inhibitors to block key pathways of nitrogen loss. Their regulation targets enzyme and microbial activity in the soil, rather than physically blocking nutrient release like coated fertilizers.

Urease Inhibitors (Representative Ingredients: NBPT, NPPT)

Target: Inhibits the activity of urease in the soil.

Principle: When ordinary urea is applied to the soil, urease rapidly decomposes it into ammonia nitrogen, some of which volatilizes into the air, resulting in loss. Urease inhibitors bind to urease, reducing its decomposition efficiency, slowing down urea decomposition, prolonging the residence time of ammonia nitrogen in the soil, and reducing ammonia volatilization loss.

Suitable scenarios: Suitable for alkaline soils and surface application, significantly reducing the risk of ammonia volatilization causing leaf burn to crops and air pollution.

Nitrification inhibitors (representative components: DCD, CP, DMPP)

Target: Inhibits the activity of nitrifying bacteria in the soil.

Principle: Ammonia nitrogen (NH₄⁺) produced by urea decomposition is gradually converted into nitrate nitrogen (NO₃⁻) under the action of nitrifying bacteria. Nitrate nitrogen is easily lost with rainwater or irrigation water and can also be converted into nitrogen gas and released under the action of denitrifying bacteria. Nitrification inhibitors can inhibit the nitrification process, stabilizing nitrogen in the ammonia nitrogen form for a longer period of time. Ammonia nitrogen can be adsorbed by soil colloids and is not easily lost.

Suitable scenarios: Suitable for rainy areas and sandy soils, reducing nitrogen leaching loss.

The current mainstream stabilized fertilizers mostly employ a dual-inhibitor combination technology, combining urease inhibitors and nitrification inhibitors. This simultaneously blocks two pathways: “urea decomposition → ammonia volatilization” and “ammonia nitrogen nitrification → nitrate nitrogen loss,” resulting in superior nitrogen retention and a 20%-30% increase in nitrogen utilization compared to ordinary urea.

II. Core Advantages

Lower Cost and Simpler Process: The production of stabilized fertilizers does not require complex coating or chemical synthesis processes. Inhibitors are simply added during the mixing stage of ordinary fertilizer production. Production costs are significantly lower than polymer-coated controlled-release fertilizers, offering higher cost-effectiveness and making them more suitable for large-scale field application.

Less Nitrogen Loss and Higher Utilization: Effectively reduces nitrogen loss caused by ammonia volatilization and nitrification-denitrification. Nitrogen fertilizer utilization can be increased from 30%-40% with traditional urea to 50%-60%, approaching the level of some slow-release fertilizers.

Flexible application, suitable for field crops. It can be applied as a base fertilizer in one application or as a top dressing in multiple applications, without the structural damage caused by crushing like coated controlled-release fertilizers. It is especially suitable for field grain crops such as corn, wheat, and rice, meeting the needs of large-scale mechanized fertilization.

Environmentally friendly, reducing nitrogen loss and volatilization, lowering pollution to the atmosphere (ammonia pollution) and water bodies (eutrophication due to nitrate nitrogen leaching), aligning with the agricultural policy direction of reducing fertilizer use and increasing efficiency.

III. Product Types and Applicable Scenarios

Main Product Forms

Stable Urea: Urea with added urease inhibitors or dual inhibitors, the most basic stabilized fertilizer.

Stable Compound Fertilizer: Nitrogen-containing compound fertilizer with added dual inhibitors, balancing nitrogen, phosphorus, and potassium supply with nitrogen stability, such as stabilized NPK compound fertilizer.

Dual/Multi-Controlled Fertilizers: Fertilizers with two or more inhibitors added simultaneously, suitable for different soil and climate conditions.

Applicable Scenarios

Preferred for: Field crops (wheat, corn, rice), oil crops (soybeans, rapeseed). Significantly reduces fertilizer and labor costs during large-scale planting.

Suitable Soils: Alkaline soils (reduces ammonia volatilization), sandy soils (reduces nitrogen leaching), and farmland in rainy areas.

Unsuitable Scenarios: Aquatic crops (such as lotus root), and highly acidic soils (inhibitor effectiveness will be affected). IV. Key Differences Between Stable Fertilizers and Coated Slow-Release/Controlled-Release Fertilizers

The key differences between stable fertilizers and coated slow-release/controlled-release fertilizers lie in several aspects: The former relies on the technical principle of regulating nutrient transformation through chemical inhibitors, achieving fertilizer retention by slowing down the rate of nitrogen conversion, rather than directly controlling nutrient release. Its production cost is lower, approaching that of ordinary fertilizers, and its application method is flexible, suitable for both basal and topdressing applications. The fertilizer can also be crushed for use, making it more suitable for field crops such as wheat, corn, and rice. The latter, on the other hand, is based on the technical principle of physically coating to block nutrient release, controlling the dissolution and diffusion rate of nutrients through the coating. Its production cost is higher, 1.5-3 times that of ordinary fertilizers. It is recommended to apply it as a basal fertilizer in one application, avoiding crushing to prevent damage to the coating structure. It is more suitable for cash crops such as fruit trees, flowers, and greenhouse crops.

From Inhibitor Addition to Industrial Granulation

The manufacturing of stabilized NPK fertilizers integrates inhibitor technology into the established npk fertilizer manufacturing process. The process begins with precise formulation in a npk blending machine, where nitrogen sources, inhibitors, and other nutrients are uniformly mixed. This homogeneous blend then enters the core granulation stage of a complete npk fertilizer production line. Advanced npk granulation machine technology is applied here, using equipment such as a npk fertilizer granulator machine or a disc granulator machine to form the powder into durable, market-ready granules.

The efficiency and consistency of this npk fertilizer granulator machine equipment directly impact the NPK compound fertilizer production capacity and final product quality. This integration of chemical innovation (inhibitors) with precision mechanical engineering (npk fertilizer production technology) exemplifies modern fertilizer manufacturing. It enables the scalable production of high-efficiency, environmentally considerate fertilizers that provide field crops with stabilized nitrogen nutrition, enhancing nutrient use efficiency while supporting sustainable agricultural practices.

 Introduction: How is Good Fertilizer “Forged”?

In the field, we want nitrogen fertilizer to release slowly, nourishing crops persistently, rather than leaching or volatilizing quickly. Slow-release urea fertilizers are designed for this purpose. However, manufacturing high-quality slow-release urea granules is not a simple matter of mixing and pressing. It is more akin to a precise “culinary” process, where the raw material formulation is the recipe, and the granulation process is the heat and timing. A recent study delves into how adjusting two key “switches” in a disc granulator—binder concentration and granulation time—can precisely control the final “physical fitness” of fertilizer granules, thereby providing a scientific guide for producing more efficient and environmentally friendly slow-release urea.

I. The Core of the Study: Two Variables, Four Qualities

Imagine a rotating shallow pan where urea powder and a binder solution extracted from cassava starch are mixed and tumbled. The research team set up a clear comparative experiment: they fixed all other conditions like disc speed and inclination, and systematically changed only two factors: the concentration of the starch binder solution and the time the material spends tumbling in the pan for granulation.

They focused on these four “fitness” indicators that determine fertilizer quality:
1. Durability: Are the granules “tough” enough? Can they withstand collisions and friction during long-distance transport without turning into powder?
2. Density: Are the granules “fluffy” or “solid”? This affects the actual weight per bag of fertilizer, transportation costs, and application uniformity in the field.
3. Pelletizing Yield: How much raw material successfully turns into qualified granules? This directly impacts production efficiency and cost.
4. Water Absorption and Dispersion Time: Do the granules disintegrate quickly or release slowly upon contact with water? This is the core measure of their “slow-release” capability. We want them to dissolve like a slow-release candy, providing nutrients steadily in the soil.

II. Finding One: Binder Concentration—The “Glue” Matters

Cassava starch plays the role of “natural glue” here. The study found that the thickness of this “glue” has a decisive impact on granule quality.

When researchers increased the concentration of the starch solution, a positive chain reaction occurred: the granules’ water absorption, density, pelletizing yield, and durability all improved simultaneously. This is because a thicker starch solution forms a stronger, denser binding network around each urea particle. Just like using thicker glue for bonding, the adhesion is firmer, the structure is more compact, and the granules naturally become tougher, heavier, and have fewer internal pores.

More interestingly, granules made with higher concentration starch also “held on” longer in water. They disintegrated and released nutrients more slowly, which is the dream characteristic of slow-release fertilizers. Observations under an electron microscope showed that granules from the high-concentration group had surfaces like smooth, dense pebbles, while those from the low-concentration group had rough, porous surfaces, visually explaining the source of the performance difference.

III. Finding Two: Time—The Art of “Kneading”

Granulation time is like the kneading time when making dough. The study showed that extending the “kneading” time of the granules in the disc also led to comprehensive quality improvements.

Longer granulation time gives the powder more opportunities to collide, adhere, and round off. This results in more regular granule shapes and a more compact interior. Consequently, granule durability, density, and pelletizing yield all increased with time. Simultaneously, sufficient kneading allows the starch “glue” to distribute more evenly, forming a more complete coating. This not only slightly increases the granules’ water absorption capacity but, more importantly, extends their dispersion time in water, further optimizing the slow-release effect.

IV. Insights for Producers: How to “Customize on Demand”

This study turns complex processes into clear multiple-choice questions:

• If you want to produce high-end fertilizers with optimal controlled-release performance and superior storage/transport durability, the answer is: use a higher concentration of cassava starch binder and allow for a longer granulation time.

• If you need to strike a balance between production efficiency and cost to produce the most cost-effective product, you can utilize the data models derived from research to calculate the optimal combination of binder concentration and granulation time based on your specific requirements for granule density, strength, and release period.

It’s like mastering a precise “cooking” formula, allowing fertilizer producers to flexibly “customize” slow-release urea products with different specifications and performance according to market demand.

Optimizing Granulation: The Science Behind Consistent Fertilizer Pellets

The scientific study of binder concentration and granulation time directly applies to the core of npk fertilizer production technology. In a complete npk fertilizer production line, precise formulation using a npk blending machine ensures accurate nutrient ratios. The subsequent granulation stage, which is central to the npk fertilizer manufacturing process, leverages advanced npk granulation machine technology to transform this mix. The principles of optimizing binder properties and process timing are critical for equipment like a npk fertilizer granulator machine, whether it operates as a wet granulator or an alternative system like a fertilizer roller press machine for dry compaction.

Mastering these variables allows manufacturers to fine-tune the NPK compound fertilizer production capacity and the final product’s physical properties—such as density, strength, and dissolution rate. This level of control is essential for producing high-quality slow-release or controlled-release fertilizers. The integration of this scientific understanding into the operation of npk fertilizer granulator machine equipment demonstrates how empirical research translates into practical, scalable manufacturing excellence. It enables the production of consistent, “tailor-made” fertilizers that meet specific agronomic needs, enhancing nutrient use efficiency and supporting sustainable agricultural practices through precision engineering.

Conclusion

The power of science lies in transforming experience into quantifiable, replicable laws. This study on disc granulation process, through rigorous experimentation, reveals how two ordinary operational parameters—binder concentration and granulation time—act like levers to influence the final quality of slow-release urea granules. It not only provides a direct “operating manual” for fertilizer plants to optimize production but also brings us a step closer to the goal of producing more efficient, environmentally friendly, and intelligent “ideal fertilizers.” In the future, by exploring more “variables,” we can hope to design bespoke fertilizers, like precision instruments, perfectly tailored to the needs of every crop and every plot of soil.