The appropriate particle size for organic fertilizer granules should be determined by comprehensively considering industry standards, production processes, application methods, and usage scenarios. The mainstream particle size range is 1.00-5.60mm, with specific selections as follows:

I. Industry Standards for Particle Size Specifications

1. Organic-Inorganic Compound Fertilizers (GB 18877-2009)
   • Explicitly require that 70% or more of the particles fall within the size ranges of 1.00mm–4.75mm or 3.35mm–5.60mm, ensuring product uniformity.
2. Commercial Organic Fertilizers (NY 525-2021)
   • Allow for either powdered or granular forms. While granular products must have a moisture content ≤30%, no strict particle size limits are mandated; practical production often references compound fertilizer standards.

II. Production Process Influences on Particle Size

1. Granulation Techniques
   • Disc Granulation/Extrusion Granulation: Requires finely ground raw materials with a granulation moisture content of approximately 30%. Final particle diameters are typically controlled within 3.0-4.0mm, achieving a granulation rate exceeding 70%.
   • Screening Process: Utilizes vibrating screens or trommel screens to classify particles, eliminating oversized or undersized granules and ensuring size uniformity.
2. Production Equipment Constraints
   • Factors such as die bore diameters in granulators and drying efficiency influence achievable particle size ranges, with common equipment supporting adjustable sizes from 1-6mm.

III. Matching Particle Size to Application Methods

1. Base Fertilizer Application
   • 3-5mm granules are suitable for soil incorporation or hole application, offering strong resistance to breakage and prolonged nutrient release.
   • 1-2mm micro-granules can be used in drip irrigation systems to prevent clogging.
2. Topdressing Application
   • 2-4mm granules facilitate机械化 spreader application, reducing dust pollution.

IV. Particle Size Selection for Specific Usage Scenarios

1. Potted Flowers
   • 2-4mm granules are ideal for mixing with garden soil or coconut coir, minimizing root burn risks.
2. Orchards/Fields
   • 3-5mm granules are optimal for机械化 deep placement, reducing volatilization and extending fertilizer efficiency.
3. Controlled Environment Agriculture
   • 1-3mm granules are suitable for soilless cultivation substrates, enhancing root nutrient absorption.

V. Specialized Adjustments for Specific Needs

• Slow-Release Fertilizers: Particle sizes can be increased to 5-6mm, with coating technologies employed to prolong nutrient release cycles.
• Water-Soluble Fertilizers: Particle sizes may be reduced below 1mm, though organic fertilizer solubility limitations must be considered.

VI. Conclusion

• General Recommendation: 3.0-4.0mm granules are recommended, balancing granulation efficiency, breakage resistance, and application convenience.
• Flexible Adjustments: Tailor particle sizes based on crop type (e.g., smaller granules for succulents, larger granules for fruit trees), application method (mechanical vs. manual), and environmental conditions (e.g., larger slow-release granules in arid regions).

It is advisable to conduct pilot-scale trials before full-scale production to determine the optimal particle size and clearly label product specifications to guide users in scientific application practices.