Soil air is a continuation of the atmospheric air. Unlike the other
components, it is constant state of motion from the soil pores into the atmosphere
and from the atmosphere into the pore space. This constant movement or
circulation of air in the soil mass resulting in the renewal of its component gases is
known as soil aeration. .
Composition of Soil Air: The soil air contains a number of gases of which
nitrogen, oxygen, carbon dioxide and water vapour are the most important. Soil air
constantly moves from the soil pores into the atmosphere and from the atmosphere
into the pore space. Soil air and atmospheric air differ in the compositions. Soil air
contains a much greater proportion of carbon dioxide and a lesser amount of
oxygen than atmospheric air. At the same time, soil air contains a far great amount
of water vapour than atmospheric air. The amount of nitrogen in soil air is almost
the same as in the atmosphere.