How to measure soil respiration and interpret results

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 by laboratory analysis or in-field.

Solvita® respiration burst (CO₂-C) measures the amount of carbon dioxide (CO₂) released by soil microbes when a dried soil is rewetted. 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.

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
• Test the soil using one of two approaches:
  • Send to a laboratory to arrive next day (if not practicable, store in a refrigerator and dispatch within 24 hours)
  • Use a DIY basal soil respiration kit yourself as soon as possible

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.

The soil health scorecard contains benchmarks for laboratory 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.

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.

Watch this short video to find out how to do the in-field soil respiration test.