The Salt Index - What is it? Why is it Important?

What is the Salt Index?

The Salt Index, or SI, is a numeric ratio between the increase in osmotic pressure produced by a specific fertilizer product compared to that produced by the exact weight of Sodium Nitrate.
Osmotic pressure needs to be applied to a pure solvent to prevent the solvent from passing into a solution via osmosis.  Osmotic pressure indicates the strength of salt solutions in competition with plant roots for water. Various fertilizers have different salt indexes, which show the probability of fertilizer burn.


How is the Salt Index Measured?

Although Salt Index (SI) represents the osmotic pressure exerted by a fertilizer product, this is very difficult to measure. Hence the fertilizer sector came with the Sodium Nitrate reference system. Sodium Nitrate has a value of 100, and all other fertilizer components are gauged accordingly. The Sodium Nitrate standard allows the salt index for a blended fertilizer to be calculated or measured.