Soil CO₂ concentrations and their implications in conventional and no-tillage agricultural fields

Soil CO₂ concentrations to a depth of 50 cm depth were monitored with Vaisala CO₂ probes from June 2004 to May 2005 in conventionally plowed and no-tillage agricultural plots and found to be generally higher in the former than the latter. Soil CO₂ concentrations were also higher in summer and lower in winter, but were modulated by harvesting and the application of crop residues. Analysis of diurnal variations in soil CO₂ concentrations, soil CO₂ effluxes, and soil temperatures revealed distinct differences between plots. The relative amplitudes of the variation in CO₂ concentrations peaked at a soil depth of 5 cm. Soil CO₂ concentrations were higher when there was higher soil water content after precipitation, while soil CO₂ effluxes were lower under the same circumstances. These two results relate to the lower diffusivity at higher soil water content, which restricts CO₂ efflux, leading to higher soil CO₂ concentrations. Calculations reveal that in the shallower soil layer (0-5 cm), CO₂ production was greater in no-tillage plots, whereas in the deeper layer (15-25 cm), it was greater in conventional plots.