Measurement of Air Space in Soil

Rationale

Soil air and roots

A very important component of soils is the air space (pores, voids and cracks) between the soil particles and between the aggregates. It is in these air spaces where all the action, such as water and air movement, takes place. It is where soil organisms live and work. It is where plant roots grow. Roots need air to breathe and the air spaces make it possible for the roots to spread out in search of food. (Extract from Farmer Field Schools Facilitators' manual)

The amount of air space in the soil at a location is thus an important soil physical property. This
experiment gives a simple method to measure it.

Hypothesis or Theory

The amount of air space will depend upon the size and shape of the soil particles, how they have been managed and the vegetation and water in the volume.  When a known volume v of  soil with air spaces a, is mixed with the same volume of water v, then the air in the soil escapes and the volume of the mixture, will be 2v­a.  Thus a can be measured and the air space density calculated as a/v.

Methodology

The method is directly taken from:

Farmer Field Schools Facilitators' manual
Vol 1, Integrated soil, water and nutrient management in semi arid Zimbabwe
O. Hughes and J.H.Venema (eds), 131 pages,
Dept of Agricultural Research and Extension, and  FAO of the UN
Harare, Zimbabwe,  Feb 2005

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