Assessment of soil moisture influence on CO2 flux: a laboratory experiment.

Accurate measurements to assess the influence of soil moisture on CO₂ flux requires the absolute estimates of soil CO₂ flux. Thus, it was constructed a calibration system where CO₂ with fixed concentration flowed through the different porous material. Previous to measurement, in order to verify the performance and reliability of a closed dynamic chamber, different discontinuous air-mixing rates and times were tested. The CO₂ flux was estimated through sequential lectures and the best fit for flux measurements was obtained taking short readings every 3 min, during a total time of 12 min ( R² = 0.99). The best mixing rate was attained for 250 mL min⁻¹, allowing 25 s of mixing previous to CO₂ extraction for an infrared gas analyzer. The deviation of the measured values for dry sand from the reference CO₂ flux (0.097 and 0.071 g m⁻² min⁻¹) was 5 and 7%. On dry sandy loam soil (SLS) the deviation was 2%. The measured fluxes decreased 73 and 22% with content moisture of 20 and 10% (sand), and 78% with content moisture of 31% (SLS). This work allowed to estimate how much the measured emission rates deviate from the true ones for the specified chamber and sampling conditions. [ABSTRACT FROM AUTHOR]