20. Cracking clay soils/Low elevation plateaux: Low relief, low drainage density

These soils have developed on associated alluvium and colluvial material of Neogene sands (often indurated) in the Western Uplands, predominantly on the Dundas Tableland. The soil has an acidic surface but the subsoil is alkaline not far below the surface horizon.

The surface soil is usually a dark (occasionally self-mulching) light to light medium clay which is structured. This may overlie an occasional bleached subsurface horizon. These soils have strong consistence (strength) depending on moisture condition. There is a clear change to a dark grey, heavy clay. It has strong structure (with medium parting to fine sized peds), becoming more yellow in colour and with slickensides at depth. This soil grades into lighter textured weathered alluvium parent material. The profile depth is about 180 cm or more with variable depths of the surface horizons, generally 5 cm for the surface and 10 cm for the subsurface, occasionally deeper.

Notable features include:

• Cracking clay soil, variable surface friability (coarser pedality).
• Strong consistence (strength) when dry.
• Occasional ferruginised nodules (buckshot) and calcium carbonate at depth.
• Yellow hued subsoil has restricted soil drainage, generally sodic at depth.