What is the qualified particle size of sulfur-based NPK compound fertilizer?
The qualified particle size of sulfur-based NPK compound fertilizer should be 2–4 mm rounded particles. This is the commonly implemented particle size control standard in the production process of sulfur-based NPK compound fertilizer, and it is also the mainstream product specification for the low-temperature conversion spray granulation process of potassium chloride in China. Within this particle size range, the product has a uniform, rounded granule appearance, and the particle size compliance rate of some high-quality products can reach over 97%.
I. Why 2–4 mm?
This particle size specification is the result of the combined effects of fertilizer production and agricultural application needs: Uniform Mechanical Spreading: 2–4 mm particles are of moderate size and have good flowability, making them less prone to segregation during mechanical spreading, thus achieving uniform fertilization.
Stable Nutrient Release: Particles within this size range have a moderate specific surface area, ensuring a reasonable nutrient release rate in the soil without the risk of rapid dissolution and loss due to excessively small particles or slow release due to excessively large particles.
Meets industry standards: Although the national standard GB/T 15063-2020 requires compound fertilizers to have a particle size of (1.00–4.75mm or 3.35–5.60mm) ≥90%, sulfur-based NPK compound fertilizers typically adhere to a stricter 2–4mm internal control standard in actual production to ensure product particle uniformity and market competitiveness.
II. How is particle size controlled?
During production, the granulated material undergoes a screening process for grading control: Particles larger than 4.2mm: crushed and returned to the granulator for reprocessing; Fine powder smaller than 2.0mm: returned to the granulation system via a return pipe; Particles within the 2.0–4.2mm range: processed as finished products for cooling, coating, and packaging.
This closed-loop screening and return system ensures that the particle size of the final product is strictly controlled within the 2–4mm range.
When purchasing sulfur-based NPK compound fertilizers, users can use particle size as one of the most direct indicators of product quality. High-quality products should have uniformly sized particles, smooth surfaces, and no obvious dust. It is also recommended to pay attention to the implementation standards and total nutrient content (usually around 45%) indicated on the product packaging.