Soil Air | Its Composition and Importance in Plant Growth

Air present in between the pore space of soil is called soil air. This soil air helps grow the aerobic organisms present in the soil.

Soil air is found between crumbs called inter-crumbs pores and pores within the crumbs called crumbs pores.

soil air

A well-aerated soil is one in which gases are available for the growth of plants, and the macro or microorganisms present in it. However, soil aeration is affected by excess moisture present in soil and gaseous exchange.

Reasons for poor aeration

  • Soil moisture – when soil receives an excessive amount of moisture, waterlogging conditions develop. This condition generally occurs due to poor drainage and fine-textured soil with minimum macropores. It also occurs in well-drained soil when there is an excess water supply. These can affect the growth of the plant and also the useful organisms present in the soil.
  • Gaseous exchange – the improper exchange of gases between the soil and the atmosphere can affect soil aeration. The gaseous exchange takes place due to the diffusion process.

Composition of Soil Air

The gaseous composition of soil air is quite similar to the atmospheric air. It varies only in terms of carbon dioxide, which is higher than that in the atmospheric air.

Further, the soil air compositions vary from location to location.

Name of gasSoil air (% Vol)Atmospheric air (% Vol)

This soil air supports the life of plants and other organisms present in the soil. The aerobic organisms and roots of the plant consume oxygen and release carbon dioxide.

Characteristics of Soil Air

There are various parameters that are used for characterizing soil aeration

  • Composition of the soil
  • The oxygen diffusion rate (ODR)
  • Oxidation-reduction potential, indicating the oxidized or reduced condition of the soil.

Factor Affecting the Composition of Soil Air

The composition of soil air is affected by a variety of factors like physical properties of the soil condition, types of vegetation, sessions, amount of organic matter and microbial activity, depth of the soil, and temperature.


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

The depth of the soil also modifies the amount of oxygen in the soil, and with the increase in the depth, the availability of oxygen decreases. The composition of soil air is also affected by seasonal variations. In the dry season or summer season, the quantity of oxygen is usually higher than that of the rainy season. The cultural and other soil management practices affect the composition of the soil air by modifying the physical properties of soil like bulk density, porosity, etc.,

Carbon dioxide

CO2 in the soil is released due to the decomposition of organic matter. Therefore, the concentration of carbon dioxide is high in the soil as compared to the atmosphere. The concentration of CO2 in the soil is also affected due to temperature and seasonal changes. However, during the summer season, the activity of soil microorganisms is high, thereby the production of CO2.

Thus, the composition of soil air is dependent on the biochemical reactions, the availability of air space, and gaseous interchange.

Water vapor

The content of water vapor is much more in the soil as compared to the atmospheric air. The capillary water in the soil saturates the soil air with water vapor. If the soil moisture falls below the hygroscopic coefficient, the water vapor decreases. Irrigation is necessary for the growth of crops and so the soil remains moist during the crop growth period.

Importance of soil air

Soil air plays a very vital role in modifying the soil’s physical, chemical, and biological environment, which influences plant growth and also the yield.

The importance of soil air-

  1. Growth and development of plants and their parts – the growth of plants is fully dependent on the soil and its physical, chemical, and biological properties. Poorly aerated soil can harm the plant and its root development. Water and nutrient absorption will be affected due to poor development of roots.
  2. Microbial population and activity- soil aeration influences the activity of soil microorganisms and also affects the rate of decomposition of organic matter. The poorly aerated soil decreases the microbial as well as oxidation of organic matter. This decrease may be due to a lack of oxygen and the presence of more carbon dioxide. The biological process carried by different microorganisms, such as the decomposition of organic matter and biological nitrogen fixation, is largely dependent on the availability of soil air. The microorganism’s population is affected by soil aeration.
  3. Production of toxic substance – The production of toxic substances occurs due to incomplete decomposition of organic matter or due to poor aeration and excess amount of soil moisture(rainfall, excessive irrigation) which leads to the production of toxic organic compounds such as lactic, butyric acid, etc. this affects the plants roots and which affect their nutrient absorption process.
  4. Absorption of water and nutrients – The soil aeration also affects the uptake of nutrients by plants. The nutrient availability varies in the soil in response to the aeration which changes the metabolic status of the plants. There is a deficiency of micronutrients like Cu and Zn under poor aeration or waterlogged conditions.

Importance of Soil Air

Aeration can improve the soil’s physical properties like

  1. Texture
  2. Density
  3. Structure
  4. Porosity

Aeration can improve soil’s biological properties

A variety of organisms inhabit the soil. They decompose organic matter, fix the atmospheric nitrogen, cause denitrification, etc. Such activities may be beneficial for the crop and its yield.

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