24. Cracking and self-mulching clay soils/Older alluvial plains: Plains with and without leveed channels

These soils have developed on alluvium of Quaternary unconsolidated material in the Northern Riverine Plains, predominantly on the Wimmera River prior stream plains. This soil is alkaline throughout.

The surface soil is a dark greyish brown light to medium clay, which is subplastic and self-mulching (occasionally moderately structured). These upper soils have strong consistence (strength) depending on moisture condition. There is a clear change to a dark grey (occasionally grey) medium to heavy clay. This upper subsoil is weakly structured (fine sized peds) but coarsely structured below the upper subsoil. It is subplastic, often with calcium carbonate and is sodic (occasionally high in the profile). The profile depth is about 2 m or more grading into fine alluvial sediments with variable depths of the surface horizons, generally 5-15 cm for the surface soil.

Notable features include:

• Cracking clay and self-mulching soil, variable surface friability (mainly self-mulching).
• Strong consistence (strength) when dry.
• The soil is sodic, occasionally including the surface and strongly sodic at depth, as well as some calcium carbonate nodules and soft segregations.
• Restricted drainage when moist (shrink-swell, slickensides).