1. Nature and condition of soil: The quantity of oxygen in soil air is less than that
in atmospheric air.
The amount of oxygen also depends upon the soil depth.
The oxygen content of the air in lower layer is usually less than that of the surface
soil. This is possibly due to more readily diffusion of the oxygen from the
atmosphere into the surface soil than in the subsoil.
Light texture soil or sandy soil contains much higher percentage than heavy soil.
The concentration of CO2 is usually greater in subsoil probably due to more
sluggish aeration in lower layer than in the surface soil.
2. Type of crop: Plant roots require oxygen, which they take from the soil air and
deplete the concentration of oxygen in the soil air. Soils on which crops are grown
contain more CO2 than fallow lands. The amount of CO2 is usually much greater
near the roots of plants than further away. It may be due to respiration by roots.
3. Microbial activity: The microorganisms in soil require oxygen for respiration
and they take it from the soil air and thus deplete its concentration in the soil air.
Decomposition of organic matter produces CO2 because of increased microbial
activity. Hence, soils rich in organic matter contain higher percentage of CO2
.
4. Seasonal variation: The quantity of oxygen is usually higher in dry season
than during themonsoon. Because soils are normally drier during the summer
months, opportunity for gaseousexchange is greater during this period. This
results in relatively high O2
and low CO2
levels.Temperature also influences
the CO2
content in the soil air. High temperature during summerseason
encourages microorganism activity which results in higher production of CO2