8. Cracking clay soils/Dissected Uplands: Eruption points an d volcanic plains

This soil has developed mainly on Quaternary basic (basaltic) volcanics in the Western Uplands. Some areas have had varying amounts of sand covering the basaltic material. These soils often have slightly acidic to neutral surface horizons becoming neutral to alkaline with depth.

The surface soil is usually a dark brown (occasionally self-mulching) clay loam to heavy clay with moderate structure (with fine to medium sized peds). It occasionally overlies a bleached subsurface horizon (local gilgai feature) with common ferruginised nodules. There is a clear change to a brown to yellow brown, heavy clay upper subsoil horizon. This is strongly structured (coarse sized peds), parting to weakly structured (medium sized peds) with ferruginised nodules in the upper and mid subsoil, becoming more mottled (light grey and yellowish red) in colour and with slickensides with depth, and grades into weathered parent material (basalt). The profile depth is about 120 cm or more with variable depths of the surface horizons, generally 1-10 cm for the surface and 10 cm for the subsurface, occasionally deeper.

Notable features include:

• Cracking clay soil.
• Variable surface friability (occasional apedal surface, generally pedal).
• Very strong consistence (strength) when dry, particularly the subsoil.
• Ferruginised nodules (buckshot) in the upper soil and occasional calcium carbonate at depth.
• Yellow hued subsoil has restricted soil drainage, generally sodic at depth.