NPK blending fertilizer produciton lines operate by physically mixing various granular single-nutrient fertilizers; they eliminate the need for granulation or drying processes. These lines are compatible with a wide range of granular nitrogen (N), phosphorus (P), and potassium (K) base fertilizers, while also allowing for the optional addition of secondary nutrients, trace elements, and organic additives. Nitrogen sources primarily include granular urea, ammonium chloride, and ammonium sulfate; urea offers high nitrogen content and is suitable for general-purpose blends, whereas ammonium sulfate is ideal for chloride-sensitive crops, and ammonium chloride is commonly used for field grain crops—allowing for flexible selection based on the specific crop type. Phosphorus sources mainly consist of granular monoammonium phosphate (MAP) and diammonium phosphate (DAP), which are preferred due to their high water solubility; small amounts of granular single superphosphate (SSP) can also be incorporated. Potassium sources include granular potassium sulfate and potassium chloride; potassium chloride is cost-effective and suitable for field crops like wheat and corn, while potassium sulfate is specifically used for chloride-sensitive cash crops such as fruits, vegetables, and tea. Secondary nutrients and trace elements—such as granular magnesium sulfate, zinc sulfate, borax, chelated calcium, and silicon fertilizer granules—can be added as needed to supply essential calcium, magnesium, sulfur, zinc, and boron, enabling the production of specialized, functional fertilizers. For organic-enriched blends, dried and matured organic fertilizer granules or humic acid granules can be incorporated to enhance soil improvement capabilities. Strict requirements apply to raw material selection: all materials must be uniform granules, as excessive powder content leads to segregation and nutrient imbalance. Particle sizes should be as consistent as possible to prevent nutrient separation or caking after mixing. Materials with high hygroscopicity should be used sparingly to avoid moisture absorption and caking in the finished product, which could impair usability. Furthermore, the inclusion of hard impurities—such as stones or plastic—is strictly prohibited to prevent damage to the mixer, storage bins, and metering equipment. The metering and mixing systems within the production line offer high versatility, allowing for the flexible combination of various single-nutrient fertilizers to achieve specific nutrient ratios, thereby supporting the production of specialized bulk-blended fertilizers for field crops, fruits, vegetables, and cash crops.