Air permeability

When to determine air permeability

In many land use systems all over the world, soil deformation is a major problem due to increasing land use intensity. When soil functions are altered, especially reduced hydraulic conductivities and impeded aeration, this can decrease crop growth and productivity as well as the filtering and buffering capacity of soils.

The determination of the air permeability before and after static loading in oedometer tests is a commonly applied method to analyse the influence of soil compaction on its permeability.  

The determination of the air permeability is required when considering quantified data and interpretation about the pore continuity and its dependency on the matric potential, as well as the effect of mechanical stress application on events such as anisotropy of pore structure.

It's also necessary for interpretation of the pore continuity and its dependency on the matric potential, as well as the effect of mechanical stress application on the anisotropy of pore structure.

Soil permeability

Soil permeability is generally determined by the pore sizes and their connectivity. The air is stored in soil pores, and the soil pore system is dependent on the quantity, shape and continuity of pores. Air will flow easily through soil that has large pores with good interconnectivity. Small pores, even if they have the same degree of connectivity, show lower permeability because air flows through small pores more slowly.

Air permeability is also influenced by soil texture, macro-pore volume and connectivity, as well as matric potential and water content. Continuous macro-pores that would normally conduct air well fill up with water when the load increases, depending on the soil and initial water content.

When analysing the effect of soil compaction due to agricultural machinery, it’s important to correlate the air permeability with soil capacity parameters such as air-filled porosity, degree of saturation, water content, etc.