Soil Air

While the soil air consists primarily of nitrogen and oxygen, it usually contains higher concentrations of carbon dioxide than the atmosphere due to soil respiration, which depletes the soil air of O₂ and raises the content of CO₂. The exchange of O₂ and CO₂ between the atmosphere and the soil air tends to establish an equilibrium that depends on the soil respiration rate and on the resistance to gas movement through the soil. The soil pore space is filled either by soil water or soil air. If the soil begins to fill with water and becomes waterlogged, chemical and biological changes ensue as the soil becomes increasingly O₂ deficient or anerobic, which results in the reduction of oxides and hydroxides. In general the air volume assuming field capacity is 30 - 40 % for sandy soils, 10 - 25 % for loamy soils and 5 - 10 % for clayey soils.

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