How to do a Fizz Test

These are easy instructions for how to do a fizz test at home.  This test will help you determine which soil test is appropriate for your soil, Mehlich 3 or AA8.2.  Many soils around the world tend to be fizzy, especially in areas with rainfall less than 40 inches (100 cm) per year, or with soils that have a limestone or gypsum base.  Your soil may fizz if you have applied ag lime in the last 3 years or gypsum in the last 6 months.

To do the fizz test follow these steps:

  • Put two tablespoons (30 ml) of dry soil in a clean, dry bowl.
  • Add a tablespoon (15 ml) of white vinegar (5% acetic acid).
  • Listen carefully.

The amount of fizz is roughly proportional to the amount of carbonate or gypsum in the soil. If you have to put your ear right by the soil in order to hear anything and you have normal hearing, your soil is not fizzy. If you can see bubbles or easily hear fizzing, your soil is fizzy.

If you have fizzy soil, you should get an AA8.2 soil test rather than the standard Mehlich 3.  If your soil fizzes, the Mehlich 3 test may overestimate the amount of calcium in the soil, which throws off the TCEC calculation and the cation balance.  Naturally fizzy soils are referred to as calcareous and require special testing.