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Soil Aeration

	Soil Aeration Major gases in the atmosphere are also found in soil. There are three important gases in the soil. They are nitrogen (79%), oxygen (18-20%) and carbon dioxide (1-10%). Soil CO2 is higher than atmospheric CO2, It is a mechanism of rapid exchange of oxygen and carbon dioxide between soil pore space (macro space) and the atmosphere in order to prevent the deficiency of oxygen and toxicity of carbon dioxide in the soil air. Compact soils of fine texture may suffer from poor aeration due to water logging (gaseous exchange may not be so rapid to remove CO2 from soil air and to supply oxygen to the roots). This also happens when there is an excessive amount of readily decomposable organic matter added to the soil. Ploughing the soil during cultivation may prevent such a condition.
Soil aeration is accomplished by two methods: mass flow and diffusion. During mass flow, there is a movement of air en masse in between the atmosphere and the soil, i.e. during the day, soil is hotter than the atmosphere and the soil gases expand and pass to the atmosphere rapidly. During the night the soil gets cooler than the atmosphere and the gases flow into the soil en masse from the atmosphere. Most of the gaseous exchange in the soil takes place by diffusion mechanism. Each gas in the atmosphere exerts its own partial pressure in relation to the volume of air.
Atmosphere has a high amount of exchangeable oxygen than soil, thus the partial pressure of oxygen is more in the atmosphere than in the soil. Hence there is a movement of oxygen from the atmosphere to the soil (gases move from an area of high partial pressure to an area of low pressure). In contrast, the level of carbon dioxide in soil is more (due to the respiratory release of the soil micro-and macro flora and fauna) than that found in the atmosphere. Hence there is movement of this gas from the soil to the atmosphere. Thus there is a displacement of both the gases between the soil and the atmosphere thus facilitating gaseous exchange. Organic matter, depth and soil moisture have a role to play in influencing the soil aeration.

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