Soil Air: Composition and Relation

After reading this article you will learn about Soil Air:- 1. Composition of Soil Air 2. Factors Affecting the Composition of Soil Air 3. Soil Air in Relation to Soil and the Crop Management.

Composition of Soil Air:

The soil air contains a number of gases of which nitrogen, oxygen carbon dioxide and water vapour are the most important. Soil air constantly move from the soil pores into the atmosphere and form the atmosphere into the pore space.

Although soil air and atmospheric air differ in the compositions, soil air contains a much greater proportion of carbon dioxide and a lesser amount of oxygen than atmospheric air. At the same time, soil air contains a far greater amount of water vapour than atmospheric air. The amount of nitrogen in soil air is almost the same as in the atmosphere (Table 3.1).

Factors Affecting the Composition of Soil Air:

The composition of soil air is influenced by a number of factors such as nature of soil, soil condition, type of crop, microbial activity, season etc.

Oxygen:

The quantity of oxygen in soil air is less than that in atmospheric air. Plant roots and various microorganism require oxygen which they take from the soil air, thus, depleting the concentration of oxygen in the soil air.

The amount of oxygen also depends upon the soil depth. The oxygen content of the air in lower layer is usually less than that of the surface soil. This is possibly due to the more readily diffusion of oxygen from the atmosphere into the surface soil than in the sub-soil.

The quantity of oxygen is usually higher in dry season than during the monsoon. Because soils are normally drier during the summer months, opportunity for gaseous exchange is greater during this period. This results in relatively high O₂ and low CO₂ levels. Light texture soil i.e., sandy soil contains much higher oxygen percentage than heavy soil.

Carbon dioxide:

Decomposition of organic matter produces CO₂. Hence, soils rich in organic matter contain higher percentage of carbon dioxide. Production of CO₂ is associated with microbial activity, CO₂ increases with the increasing number and activity of microorganism.

Temperature and season also influence the carbon dioxide content in the soil air. High temperature during summer season encourages microorganism activity which results in higher production of CO₂. Soils on which crops are grown contain more CO₂ than fallow lands. The amount of CO₂ is usually much greater near the roots of plants than further away. It may be due to respiration by roots. The concentration of CO₂ is usually greater in sub-soil probably due to more sluggish aeration in lower layer than in the surface soil.

Water vapour:

Soil air, however, contains much more water vapour than atmospheric air. Capillary water in the soil is used to saturate the soil air with vapour. If the soil moisture falls below hygroscopic coefficient, the water vapour begins to decrease. During crop growing period, when soil remains moist, the amount of water vapour in the soil air would be more.

Soil Air in Relation to Soil and the Crop Management:

Soil Management:

The maintenance of a stable soil structure is an important means of augmenting good aeration. Pores of large size, are soon drained of water following a rain, thereby allowing gases to move into the soil from the atmosphere. Maintenance of organic matter by addition of Farm yard Manure and crop residues and by growth of legumes is perhaps the most practical means of encouraging aggregate. Stability, which, in turn, encourages good drainage and better aeration.

In heavy textured (clay) soil, it is very difficult to maintain optimum aeration. Aeration in the soil can be added by controlling weeds and tilling the heavy soil. Consequently, no tillage (zero tillage) or minimum tillage practices, which the quite satisfactory on well-drained soils, have limitations on poorly drained soils.

Crop management:

Selection of crop is important criteria for adaption of crop in the soil. Alfalfa, fruits and forest trees and other deep-rooted plants require deep, well- aerated soils, such plants are sensitive to a deficiency of oxygen, even in the lower soil horizon.

In contrast, shallow-rooted plants, such as grasses, clovers etc. do well on soils that tend to be poorly aerated, especially in the subsoil. The rice plant flourishes even when the soil is submerged in water.