Dispersible clay

Caution: Dispersible soils are easily damaged with tillage, compaction, lack of plant cover and from increasing salinity or acidity. Waterlogging is a major threat.

Dispersible soil loses its structure and just dissolves in water. The bonds between the particles are not strong enough to keep the particles together when wet. The soil crumbs or blocks separate into single particles.

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So when it gets wet, the clay can disperse into a liquid or gel form. The soil above the dispersed clay is then prone to collapsing into the hole left by the dispersion of the clay.

Dispersible subsoils swell when wet and this can limit infiltration and as a result drainage of the topsoil through the subsoil. This can lead to waterlogging and can also lead to erosion by dispersion.

A dispersible clay is sometimes also called a spewy clay.

Dispersion is also called deflocculation. The opposite of it is flocculation.

Spotting dispersible soil on your land

Dispersible soil may have these factors
Condition	Appearance or signs	Cause
Tunnel erosion	The erosion starts in the subsoil, then the topsoil may collapse into it. You may be able to see these tunnels running into the erosion gullies, stream banks etc	Dispersible topsoil and/or subsoil
Erosion gullies with undercut soils	Undercut soils at the sides and head of the gully. In extreme cases downstream of this there will be a moonscape of eroded topsoil, eroding subsoil and exposed bedrock	Dispersible topsoil and/or subsoil
Pugging is a problem	Pugging is a problem in the wet season and in wet areas	Dispersible topsoil and/or subsoil
Tendency to crust	Crust forms on surface of soil - surface becomes smooth and hard after wet periods	Dispersible topsoil

Testing soil to find out whether it is dispersible

Gently place a crumb (3-6 mm or 1/8 to ¼ inch across) of dry clay into some distilled water or rain water in a clean, well-rinsed glass. Do not use ground water, bore water or town water as the chemicals in them can mean the test will give a meaningless result.
Do not stir, shake or move. just let it sit for one to two hours, checking from time to time to see whether there have been significant changes.
Without moving the glass, examine the water.
- If the soil crumb is still visible and the water is basically clear, it has not dispersed.
- If it is cloudy and the soil crumb has gone, it has dispersed into the water. If so, the soil is dispersible and requires particular care. Note: If you do not keep an eye on the test, the crumb may disperse and then the dispersed soil particles may settle to the bottom. If this happens, repeat the test with enough soil to cover the bottom of the glass to a depth of several cm or one inch and note the effect and any differences. The soil will most likely settle in distinct layers.

Dispersion can be the result of

Low organic matter levels in the soil
High sodium (or lithium) levels in the soil.
Working the soil too wet or dry, particularly if the soil is low in organic matter or has high sodium (or lithium) to start with. This is worsened by more frequent workings.

Improving dispersible clay soils

Depending on your soil, financial and other situation plus the availability and cost of soil amendments, you may be able to improve the soil with the following methods

minimize tillage including minimizing non-inversion tillage
maintain a permanent sod if it is an orchard, vineyard, forest etc
maintain a permanent pasture cover
add gypsum or lime
minimize compaction, pugging, overgrazing and physical damage by using sensible and sensitive farming and grazing management
increase surface litter and roughness as well as maintain ground cover at or near to 100% to maximize infiltration while minimizing the risk of erosion
replace farming or grazing with orchards, vineyards, forests or agroforests.

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This page was updated on December 27, 2007