Enter the concentration, weight, solubility, and volume into the calculator to determine the Fertilizer Salt Index.

Fertilizer Salt Index Formula

The following formula is used to calculate the Fertilizer Salt Index. 

FSI = (C * W * S) / V

Variables:

  • FSI is the Fertilizer Salt Index
  • C is the concentration of the fertilizer (mg/L)
  • W is the weight of the fertilizer (g)
  • S is the solubility of the fertilizer (g/L)
  • V is the volume of the solution (L)

To calculate the Fertilizer Salt Index, multiply the concentration of the fertilizer by the weight of the fertilizer, then multiply the result by the solubility of the fertilizer. Divide the result by the volume of the solution.

What is a Fertilizer Salt Index?

The Fertilizer Salt Index is a measure used to determine the salt concentration in a fertilizer solution. It is important because high salt concentrations can cause damage to plants, including burning and dehydration. The index provides a way to compare the potential salt damage from different fertilizers, helping farmers and gardeners make informed decisions about which fertilizers to use. The lower the salt index, the less potential for salt damage to crops.

How to Calculate Fertilizer Salt Index?

The following steps outline how to calculate the Fertilizer Salt Index (FSI).

  1. First, determine the concentration of the fertilizer (C) in milligrams per liter (mg/L).
  2. Next, determine the weight of the fertilizer (W) in grams (g).
  3. Next, determine the solubility of the fertilizer (S) in grams per liter (g/L).
  4. Finally, determine the volume of the solution (V) in liters (L).
  5. Using the formula FSI = (C * W * S) / V, calculate the Fertilizer Salt Index.
  6. After inserting the values of the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

concentration of the fertilizer (C) = 50 mg/L

weight of the fertilizer (W) = 100 g

solubility of the fertilizer (S) = 10 g/L

volume of the solution (V) = 5 L