Quantifying Soil Emission Rates of Carbon Dioxide using Nighttime Observations of Atmospheric Pooling

Quantifying soil emission rates of carbon dioxide using nighttime

observations of atmospheric pooling.

1. B. Hicks^a,b, J. N. Oetting^b and N. S. Eash^b

^a Metcorps, Norris, Tennessee

^b Institute of Agriculture, University of Tennessee, Knoxville, Tennessee

There are countless studies of emission rates of CO₂ from soils using chambers. In all such experiments there is a need to correct for effects of the chambers’ physical presence. Observations of nocturnal pooling of CO₂ effluxes offers an opportunity to evaluate effluxes without the use of chambers. The methodology uses short-term measurements of CO₂ concentrations closely above the surface in conditions of quiescent stratification, such as often occur at night when crops are growing. Studies of CO₂ pooling in the atmosphere within and above a maize canopy have been subjected to statistical analysis that reveals emission rates much as expected, hence serving as a chamberless verification of legacy conclusions. In the earlier part of the year, efflux rates varied considerably around a slowly rising value starting at about 0.03 μmol m^-2 s^-1 in winter and peaking at about 5 μmol m^-2 s^-1 in mid-summer. The detail yielded by the short-term measurements (based on 5–min averages made almost continuously over the years 2017 and 2018) indicates that the Q10 value for the study area was slightly above 2.0 during the period of major microbial activity, when soil temperatures were between about 20⁰C and 30 ⁰C. In mid-winter, when subsurface soil was frozen, bursts of warm weather appear to have caused thawing of near-surface soil, thus permitting previously sequestered gaseous CO₂ to escape to the surface. The soil temperature dependence of the computed efflux rates is the most statistically significant feature of the dataset.