A fizz test is a simple screening tool that can be used as a first
step to help identify on-farm lime sources.
It involves adding dilute hydrochloric acid to soil and observing the reaction. If the
soil fizzes, then it contains carbonate or gypsum – hence the name fizz test.
In this video, Stephen Lawrence from GHD demonstrates how to do a fizz
test and interpret the results to help make informed decisions about on-farm lime sources.
To get started, it’s important to have a number of items:
A flat benchtop or table in an open space with airflow
Soil sample – 1kg bulk sample from each area of interest
Protective clothing including gloves and safety glasses
Measuring spoons Container for soil sample
A coarse sieve A glass or acid resistant measuring jug
A mortar and pestle or some means of crushing the soil
Non-metallic saucers or dishes for testing the soil sample
Non-metallic stirrers Dilute hydrochloric acid - approximately 1 molar
Capped bottle and dropper for dilute HCL
Data sheet to record results Paper towel
Container or bucket for disposing of tested soil and acid
Distilled or deionised water in a squirt bottle First aid kit with eye wash, just in case.
The first step is to prepare the soil sample for testing.
For this example we’re using soil sourced from a property in Western Australia.
The soil has been put through a coarse sieve to remove any oversized organic material or rocks.
Take 1 tablespoon of the subsample and crush it up using a mortar and pestle
or put it in a plastic bag and use a hammer or rolling pin.
Grinding the sample helps increase the surface area of any carbonate nodules
and promote a more uniform reaction with the acid.
Take about half a teaspoon of the crushed sample and spread it out evenly on a dish.
The next step is to add the dilute hydrochloric acid – if the soil fizzes
then it is likely to contain carbonates, hence the name Fizz test.
Start by adding three to five drops and see if the reaction takes place. There are
three key observations to note down - they are: The visible reaction – does it bubble and fizz
and if so, is it strong, moderate or slight? Any audible sound – the reaction might make
a fizzing noise, though not always. Soil movement – did the sample expand
or spread out on the dish? This can help indicate the level of reaction.
Once you’ve made your observations, add a few extra drops to gradually cover the sample,
then stir and observe.
Again, note down the visual reaction and any sound.
It’s important to allow sufficient time for the reaction to occur, as some carbonate
minerals may react more slowly than others – for example dolomite compared to calcite.
That’s the end of the fizz test.
There is a scale rating to help interpret results – each sample
can be given a fizz rating of one to five. One being no audible or visible
fizz reaction – and five being strong visible and/or audible fizz reaction.
Note that the fizz may not always be audible even if there is a visible reaction.
These samples are good examples of four and five
fizz rating. They have moderate to strong audible and visible fizz reaction.
Soil samples with a four or five fizz rating would be expected to contain the most carbonate
and may warrant further evaluation as a potential source of on-farm lime.
The next step is to follow-up with a laboratory soil test to evaluate the neutralising value,
effective neutralising value and any potential contaminants.
These samples have a fizz rating of less than three.
A fizz rating of one means there is no audible or visual reaction.
A fizz rating of two or three means the sample has a slightly audible and/or visible reaction.
If the sample has a fizz rating of three or less, then it’s an
indication that the soil is unlikely to be a suitable source of on-farm lime.
Once the fizz test is complete, rinse and wash the equipment into a suitable container with water
and dispose of appropriately.