Soil Atmosphere
The atmosphere of soil is radically different from the atmosphere above. The consumption of oxygen by microbes and plant roots and their release of carbon dioxide decrease oxygen and increase carbon dioxide concentration. Atmospheric CO2 concentration is 0.03%, but in the soil pore space it may range from 10 to 100 times that level. At extreme levels CO2 is toxic. In addition, the soil voids are saturated with water vapour. Adequate porosity is necessary not just to allow the penetration of water but also to allow gases to diffuse in and out. Movement of gases is by diffusion from high concentrations to lower. Oxygen diffuses in and is consumed and excess levels of carbon dioxide, which can become toxic, diffuse out with other gases as well as water. Soil texture and structure strongly affect soil porosity and gas diffusion. Platy and compacted soils impede gas flow, and a deficiency of oxygen may encourage anaerobic bacteria to reduce nitrate to N2, N2O, and NO, which is then lost to the atmosphere. Aerated soil is also a net sink of methane CH4 but a net producer of greenhouse gases when soils are depleted of oxygen and subject to elevated temperatures.
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Famous quotes containing the words soil and/or atmosphere:
“Forever float that standard sheet!
Where breathes the foe but falls before us,
With Freedom’s soil beneath our feet,
And Freedom’s banner streaming o’er us!”
—Joseph Rodman Drake (1795–1820)
“The meeting in the open of two dogs, strangers to each other, is one of the most painful, thrilling, and pregnant of all conceivabale encounters; it is surrounded by an atmosphere of the last canniness, presided over by a constraint for which I have no preciser name; they simply cannot pass each other, their mutual embarrassment is frightful to behold.”
—Thomas Mann (1875–1955)