Understanding Size Guide Number (SGN) in Fertilizer Prill Size
The Size Guide Number (SGN) is a key metric used in the fertilizer industry to describe the average size of fertilizer granules, commonly referred to as "prills." Knowing the SGN helps users select the right fertilizer product for their specific application, ensuring proper nutrient distribution and optimal plant health.
What Is SGN?
SGN stands for Size Guide Number. It represents the average diameter of fertilizer prills or granules in millimeters, multiplied by 100. To calculate SGN use the following equation:
SGN = Average Prill Diameter (mm) × 100
For example, a fertilizer with an average prill diameter of 1.50 mm has an SGN of 150.
How Is SGN Determined?
Fertilizer samples are passed through a series of sieves with different opening sizes. The sieve that retains 50% of the sample by weight indicates the median particle size. This median size (in mm) is multiplied by 100 to yield the SGN as seen in the equation above.
Why Does SGN Matter?
Smaller SGN leads to enhanced application uniformity. In other words, this means more prills per square foot, leading to more uniform nutrient distribution across the soil surface.
SGN and Common Uses
- Low SGN (<100): Suited for very closely mowed turf like golf greens, where fine particles can penetrate the turf canopy easily.
- Medium SGN (100–200): Ideal for fairways, tees, lawns, and sports fields with moderate to low mowing heights.
- High SGN (>200): Best for lawns and roughs with higher mowing heights, where larger particles can move through the turf without interference.
SGN is a simple but crucial number that tells you the average size of fertilizer prills. It guides users in selecting the right fertilizer for their turf or crop, ensuring even nutrient distribution and minimizing application problems. Choosing the correct SGN for your specific needs whether for golf greens, sports fields, or lawns with a premium appearance can significantly impact plant health and fertilizer efficiency.
