CO2-Burst Method – Standard Lab Protocol
Solvita CO2-Burst provides the means for commercial laboratories to easily and efficiently measure CO2 respiration from normal, dried and sieved soils. The procedure includes a specified wetting method to adjust soils close to 50% of available pore-space with water. The updated (2019) protocol contains vetted protocols to assure CO2 is within a normal 0 – 3% range for which Solvita has validated, linear response. Measuring soil CO2 respiration has never been easier than with Solvita, and the accuracy of Solvita, when used according to procedure rivals all competing methods.
How does it work?
The test includes dried, weighed samples of soil that are moistened with a specific amount of water, triggering a modest to strong flush of carbon dioxide as microbes rapidly assimilate freshly moistened soil organic matter. The burst of activity is believed to result from accumulated osmolytes plus the disturbance effect of processing soil. The amount of CO2 release is used to infer the soil’s biological activity, related to “soil health”. The quantity of CO2 is quantified with the Solvita Digital Color Reader 24 hours after the start, in which time most of the burst effect has expressed itself (bursts often go on for 2-3 days, but it is unnecessary to run a test that long as 1-day and 3 or 4-day are nearly perfectly correlated). Modern competing methods with KOH are advocating 3-4 days as a prerequisite for CO2 testing, but this is only because their methods, unlike Solvita, are insensitive and inaccurate for short-term 24-hr measurements. Solvita is happy to provide comparative literature. CO2-Burst is considered proportional to microbial biomass and linked to potential carbon and nitrogen mineralization. SOP available here.
Why measure CO2 respiration?
- CO2 respiration as an indicator of soil health – The quantity of CO2 release over a specific period is generally regarded as an accurate indicator of biological attributes favoring healthy soil functioning. Depleted soils tend to have very low CO2 emissions. The “turnover rate” of CO2 increases with improved management practices including cover cropping and organic amendments.
- CO2 respiration as an indicator of nutrient release – Measuring the rate of carbon exchange via soil respiration is indirectly linked to nutrient “mineralization” – the potential release of nutrients such as nitrogen and phosphorus that are components of plant residues, microbes and humus. The accuracy of the measurement depends on related factors such as C:N.
- CO2 respiration as an indicator of carbon sequestration – The inverse of respiration is sequestration: what is not released as CO2. How this works is that the quantity of CO2 actually released per soil organic is only a fraction of what is stored: therefore the greater the release of CO2 the greater the reservoir in the soil is.
How soil and plants interact
Soil and plants interact. Soil provides the environment for plant growth while plants participate in building and sustaining soils by releasing exudates during life and leaving residues behind for bacterial food. This dynamic cycle is best described as the soil-plant-biology system. In the process, some carbon is sequestered as “humus” and some released as carbon dioxide (CO2) due to microbes eating. The relationship between these processes is the bedrock of lasting soil fertility. Declining rates of CO2 respiration are principally associated with the absence of sufficient plant cover to sustain soil life, and this is a result of modern farming practices. As soil quality declines, microbes food supply diminishes and the rate of CO2 respiration declines.
Why is CO2 respiration important?
Soil CO2 respiration has been known to be an indicator of soil quality since as early as the 1920’s. Research in Europe after the 50’s helped standardize lab analytical procedures even before the practical application was understood. By the 1970’s soil respiration tests were seen as useful indices to compare results of different soil management strategies. Unfortunately, it was not until more recently – with the widespread use of Solvita worldwise- that CO2 respiration was more broadly recognized to be a crucial trait linking microbial activity to healthy soil,- a complete cycle based on overall soil biota. No other test can claim this universality. In the not-too-distant future soil respiration results will provide a useful key to leveraging natural fertility to save significantly on nitrogen fertilizer dollars and help bolster farming’s environmental commitment.