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.

What to do if 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.

The soil may fizz if it has had limestone or dolomite added in the past three years. Or it may be naturally fizzy due to having a limestone base. Naturally fizzy soils are referred to as calcareous and require special testing.

You will want to determine whether the soil is calcareous or just over-limed. Read on…

How to tell if your fizzy soil is calcareous or over-limed

Calcareous soils have CaCO3 (limestone) in their parent material. In general we don’t try to drop the pH of these soils, it will take years of elemental sulfur additions. Over-limed soils have simply had too much CaCO3 applied to them, and are easy to correct using sulfur to lower the pH. A  lower pH will make minerals are more available to plants https://growabundant.com/mineral-availability-versus-ph/ so it is totally worth doing. Optimum growing conditions for plants mean more root exudates for the microbes, and a more enlivened soil.

The best way to determine whether your soil is calcareous or over-limed is to measure the pH of the surrounding unamended soils. It’s a good idea to test your unamended soil anyway. And/or, if you are in the US, accessing the Soil Web Survey can tell us if the soil is calcareous. Here’s how to do this:

  • Go to this URL: https://casoilresource.lawr.ucdavis.edu/gmap/
  • Click ‘Menu” and “Zoom to Location”
  • Sometimes just entering your address will take you to the location of your soil
  • Or, enter the decimal latitude and longitude coordinates.
**To find your coordinates, enter your address in Google maps, right click the spot and select the coordinates to copy them, then paste into the Soil Web app under Latitude and Longitude.**
  • Your location should show up on the map. Click the cursor near your location; a X with a red Circle appears.
  • Your main soil formation is under “Map Unit Composition”.  Click the top formation.
  • Click CaCO3.
  • If the topsoil has zero carbonates, the soil is over-limed and not calcareous.

Not every location in the US has been surveyed. If there is no data for your location, look at a few surrounding soil formations to see if they have CaCO3 in their soils. It is a good idea to check surrounding formations even if you do find the data for your soil. The survey data is pretty general.

While you are looking at your soil profile, there is other useful information…

Your native Organic Matter
Your native pH
Your native CEC