Importance

Good soil structure is vital for growing crops. It regulates soil aeration and gaseous exchange rates, the movement and storage of water, soil temperature, root penetration and development, nutrient cycling and resistance to structural degradation and erosion. It also promotes seed germination and emergence, crop yields and grain quality.

Good structure also increases the window of opportunity to cultivate at the right time and minimises tillage costs in terms of tractor hours, horsepower requirements and the number of passes required to prepare the seedbed.

Assessment

• Remove first the 0 – 5cm topsoil that contains dense and compacted root system without disturbing soil.
• Remove a 20cm cube of topsoil with a spade.
• Drop the soil sample a maximum of three times from a height of one metre (waist height) onto the firm base in the plastic box. If large clods break away after the first or second drop, drop them individually again once or twice. If a clod shatters into small units after the first or second drop, it does not need dropping again. Do not drop any piece of soil more than three times.
• Part each clod by hand along any exposed fracture planes or fissures.
• Transfer the soil onto the large plastic bag.
• Move the coarsest parts to one end and the finest to the other end. This provides a measure of the aggregate-size distribution. Compare the resulting distribution of aggregates with the three photographs in Figure 6.

 
Good
Moderate
Poor

Scoring

Good condition: Score 2

Good distribution of finer aggregates with no significant clodding.

Moderate condition: Score 1

Soil contains significant proportions of both coarse firm clods and friable, fine aggregates.

Poor condition: Score 0

Soil dominated by extremely coarse, very firm clods with very few finer aggregates.

References

http://adlib.everysite.co.uk/adlib/defra/content.aspx?id=000HK277ZX.0HDECKKQLJIF9JD

ftp://ftp.fao.org/docrep/fao/010/i0007e/i0007e01.pdf