Composition of Soil Air: 3 Factors

This article throws light upon the three main factors affecting the composition of soil air. The factors are: 1. Oxygen 2. Carbon Dioxide 3. Water Vapour.

Factor # 1. Oxygen:

The amount of O₂ in soil air is much less than that of the atmospheric air. Plant roots and different micro-organisms require O₂ for their metabolism which they take from the soil air and thereby decrease the concentration of O₂ in the soil environment.

The depths of soil also modify the amount of O₂ in the soil and with the increase in depth the amount of O₂ is less. This may be due to more slow diffusion of O₂ from the sub­soil horizons to the atmosphere through overlying soil layers.

The seasonal variation also affects the composition of soil air. In the dry season or summer season the quantity of O₂ is usually higher than that of the rainy season. Because in the summer season the opportunity for the gaseous exchange is greater as compared to monsoon seasons resulting high O₂ and low CO₂ concentration in the former season.

Cultural and other soil management practices affect the composition of soil air by modifying various physical properties of soil like bulk density, porosity, soil structure etc. Light texture soil contains much more O₂ than the heavy texture soil. As a rule, the higher the bulk density the more compact the soil, the more poorly defined structure and the smaller, the amount of pore spaces and restrict plant growth.

Factor # 2. Carbon Dioxide:

During decomposition of organic matter CO₂ is evolved and therefore, the concentration of CO₂ will be very high in soils high in organic matter.

There is a positive relation between the concentration of CO₂ and the activity of micro­organisms.

Temperature and season also modify the concentration of CO₂ in the soil environment. The production of CO₂ generally will be very high through increased activity of soil micro­organisms during summer season.

The cultivation of crops contributes more CO₂ in the soil air than that of fallow lands.

The concentration of CO₂ is generally higher in the sub-soil due to slower rate of exchange of gases in the lower horizon as compared to the surface soil.

Incorporation of large quantities of manure, especially if moisture and temperature are optimum, will alter the soil air composition appreciably.

So the composition of soil air is largely dependent upon the amount of air space available, rates of biochemical reactions and gaseous interchange.

Factor # 3. Water Vapour:

The content of water vapour is much more in the soil air as compared to the atmospheric air. The capillary water in the soil saturates the soil air with the water vapour. If the soil moisture falls below hygroscopic coefficient, the water vapour also decreases.

Irrigation water is necessary for the growth of crop and so soil remains moist during the crop growing period. Due to presence of moisture in the soil environment, the amount of water vapour in the soil air would be more.

The aeration requirements of crop plants vary considerably. It is, however, clear that most crop plants can grow well in a soil atmosphere with less than 21 per cent of O₂ present in the free air, whereas in the soil containing O₂ content below 10 per cent, the growth of most of the crops is restricted.