Dry Fertilizer Blending: How Granule Particle Size Distribution (PSD) Prevents Segregation

In bulk NPK dry blending factories, separate granular fertilizers (Urea, DAP, MOP, and Micronutrients) are mixed together to create customized grade ratios. However, a widespread operational failure in bulk blending is nutrient segregation during packaging, conveyor transfer, and truck transit.

1. The Physics of Particle Segregation

Segregation occurs when blended fertilizer granules differ in diameter, density, or surface friction. In transit, mechanical vibration causes small particles to sift down to the bottom of the bag, while large granules float to the top. When broadcast in the field, this results in severe uneven growth stripes—some crop rows receive excess nitrogen while adjacent rows suffer micronutrient starvation.

2. Size Guide Number (SGN) & Uniformity Index (UI)

To achieve a stable, non-segregating dry blend, all component granules must share matching physical dimensions:

• •Size Guide Number (SGN): The median granule diameter in millimeters multiplied by 100. Standard commercial Urea and DAP have an SGN of 200 to 280 (2.0 to 2.8 mm).

• •Auron Matching Granules: Auron Granular Zinc Sulphate 33% and Ferrous Sulphate Granular 30% are engineered with an SGN of 220–260, blending homogeneously with standard NPK components without sifting out.