101 Questions answered
Identifying Dispersive Soil: Simple Water Test Method
The best way to tell if you have dispersive soil is to gently place a few air-dried aggregates (peds, about 2 cm across) of soil in a dish of distilled water or rainwater. Don’t use treated tap water as it can interfere with the result.
If the water around the ped stays clear, the soil is not dispersive. If the water turns cloudy, the soil is dispersive. The cloudier the water gets, the more dispersive the soil is. Check on the soil after 10 minutes and two hours, as dispersion can take some time.
One official way is to do the ASWAT test, which uses the same process but you take readings at 10 minutes, 2 hours and 24 hours, and calculate a score of dispersion. More detail here.
If the aggregates crumble but the water does not go cloudy, this is slaking. This means that the aggregates are weak and usually low in organic matter. Slaking is not the same as dispersion.
