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Principal Binding Agents | Soil Texture | Dispersion | Slaking | Dispersion Animation

Slaking describes the break-up of dry soil aggregates into sub-aggregates as a result of rapid wetting.

Strong slaking of a dry soil

This clip shows an aggregate (of about 4 mm diameter) with a powerful slaking response. Immediately it is immersed into water, bubbles of air force their way from the body of the aggregate and produce a profusion of small bubbles. When the bubbles move away, it is seen that the aggregate has been disrupted into a heap of sub aggregates < 0.5 mm diameter.

Slaking of air dry aggregate followed by some clay dispersion

This clip shows an aggregate (also of about 4 mm diameter) which slakes rapidly but only with moderate production of air bubbles. The sub aggregates resulting are also much smaller than the previous example being < 0.2 mm diameter. Further, as time progresses, clay in the aggregates begins dispersing into the surrounding water.

What causes slaking?

Two factors cause slaking.
  • Swelling of the crystalline structure of the clay as water is rapidly adsorbed
  • Forced and rupturing escape of trapped air as capillary forces draw water into small pores between soil particles and compress the air already in the aggregate

Effect of slaking

Slaking is a consequence of rapid wetting (unlike dispersion) and is mainly a problem where large raindrops fall on susceptible dry soils. Resultant breaking apart of aggregates can reduce soil infiltration, increase runoff, and supply suitable sized pieces of soil for removal by erosion

Further information

More technical information on aggregate slaking and clay dispersion is available on VRO under ‘soil management’.
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