Soil respiration

The activity of soil microbes is a key indicator of soil health and can be measured using a simple respiration test (CO₂ burst). Soil respiration can be measured in-field or by laboratory analysis.

Respiration as a biological indicator of soil health

Progress has been made in the use of respiration as a measure of soil microbial activity, both in the laboratory and in the field. It is commonly known as the CO₂ burst test.

Microbial activity in the soil releases CO₂ that can be measured. This can provide an estimate of the soil microbial biomass.

Although measuring soil respiration is a valuable test it should be noted that biological activity varies daily, in response to seasonal changes in weather, soil temperature and soil moisture, etc. Management to improve soil biological activity is a gradual process that takes place over several years.

Any observed changes in soil biological measurements should only be considered significant when they are obvious and lasting.

Collecting a sample

You should collect a representative soil sample from the field area being tested using the standard soil sampling method described for measuring soil nutrients, pH and organic matter.

After collecting a soil sample you should:

Keep it cool and out of direct sunlight
Either test the soil yourself as soon as possible using a DIY basal soil respiration kit
Or dispatch the soil sample to arrive next day at a laboratory (if not practicable, store in a refrigerator and dispatch within 24 hours)

Laboratory analysis

Some commercial laboratories offer the CO₂ burst test and can provide guidance. For these tests, soil is dried and re-wetted to measure a burst of biological activity.

See a list of soil testing companies

Interpreting results

The soil health scorecard contains benchmarks for CO₂ burst results for grass and annual cropped fields.

However, there are current methodological issues when soil pH is above 7.5 which leads to artificially low values. In this case, you can compare within a farm with care but soils in this category cannot be compared to the soil health scorecard benchmarks.

See the soil health scorecard benchmarks

Testing soil yourself

DIY basal soil respiration tests kits are available where soil is tested in its natural state. It takes just 24 hrs to complete with minimal equipment. Soil should be moist but not waterlogged, and at a temperature of 18-24ºC, when carrying out the test.