Carbon Dioxide Burst Test - Activity. Scope and Application The “Birch effect” (Xxxxx, 1959) has long been observed as a flush, or burst, of CO2 when dry soil is rewetted. Although the mechanisms for this flush remain a topic of debate, it is widely accepted as an important metric of overall health of a soil because it has empirically been shown to be related to soil microbial biomass C (Xxxxxxxx and Xxxxxx, 1978), C availability (Xxxx et al., 2003), and to N mineralization (Fransluebbers, 1996). Care must be taken when interpreting or comparing these results because the sieving procedure, rewetting procedure, and the length of storage can all have an impact on the measured respiration response. In an effort to minimize the inter-laboratory variation and therefore enhance comparability in this metric, this protocol follows the recommendations of the Xxxxxxx group (Xxxx et al., 2018) regarding the standardization of methods related to quantification of carbon mineralization. Summary Soil is sieved to 2mm and air dried prior to starting this procedure. The soil is added to a sample cup with volumetric markers used to calculate experimental bulk density and the amount of water to use for rewetting. Immediately prior to the baseline reading a volume of water sufficient to fill 50% of the pore volume with water is added. The sample is placed inside of a quart sized jar and a baseline CO2 measurement is made. The soil is incubated with an air tight seal for 24 hours, in the dark, at 23oC and the CO2 accumulation in the headspace is measured again after 24 hours. It is very simple to add an additional 96 hour measurement if desired. Equipment and Materials Quart sized canning jar Lid fitted with a gas sampling septa 100mL sample cup Transfer Pipette 20mL gradated cylinder Deionized (DI) water Incubation chamber to maintain 23°C Picarro isotopic CO2 analyzer Procedure
