9. Sodic brown, yellow and grey texture contrast soils/Dissected Uplands: Eruption points and volcanic plains

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

The surface soil is usually a dark greyish brown, clay loam with strong structure (with fine sized peds) with weak consistence (strength). This grades into a greyish brown, conspicuously bleached clay loam upper subsurface horizon which has no structure (massive). There is an abrupt wavy change to a mottled greyish brown, clay loam lower subsurface horizon. This is weakly structured and sporadically bleached, often with many ferromanganiferous concretions. There is a clear wavy boundary to red mottled light olive brown, medium to heavy clay. This has weak to moderate structure (with coarse to medium sized peds) generally vertic (slickensides with depth). This grades into weathered basaltic regolith. The profile depth is about 120 cm or more with variable depths of the surface horizons, generally 15 cm for the surface and 20 cm for the subsurface, often deeper (0–40 cm).

Notable features include:

• Texture contrast (sharp or clear change in clay percentage with depth).
• Vertic properties (including variable topsoil depth and slickensides).
• Strongly sodic subsoil and associated dispersive characteristics.
• Lower nutrient capacity and low water holding capacity of the more acidic, lighter upper soil.
• Limited internal drainage, once moist.