ABSTRACT
At any point in time, the composition of the soil atmosphere (or soil gas phase) depends upon
(i) balance between the rates of production and consumption of various gases in the soil,
(ii) rate of exchange between the soil air and the air above the soil surface, and (iii) partitioning
of the gases between the gaseous, liquid, and solid phases of the soil. Biological processes
(e.g., respiration) normally consume O2 and produce CO2, but can also result in the release of
other gases such as nitric oxide (NO), nitrous oxide (N2O), and nitrogen (N2) during the
biological reduction of nitrate in soils. Chemical processes also can produce gases, e.g., the
volatilization of ammonia from fertilizers or the release of radon gas from the mineral fraction
of the soil.
