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:
“This fair homestead has fallen to us, and how little have we done to improve it, how little have we cleared and hedged and ditched! We are too inclined to go hence to a “better land,” without lifting a finger, as our farmers are moving to the Ohio soil; but would it not be more heroic and faithful to till and redeem this New England soil of the world?”
—Henry David Thoreau (1817–1862)
“It is better to have your head in the clouds, and know where you are ... than to breathe the clearer atmosphere below them, and think that you are in paradise.”
—Henry David Thoreau (1817–1862)