31. Sandy soils with and without pans/Siliceous dunefields: Parabolic and linear dunes

These soils have developed on Quaternary unconsolidated material (mainly aeolian) in the North West Dunefields, particularly the siliceous dunefields including parabolic and linear dunes.

The surface soil is usually a brown sand to loamy sand, which is apedal. This grades into a deep sand subsurface horizon, which is apedal (sandy) and conspicuously bleached. There is a clear to gradual change to a darker (brown) sandy subsoil horizon, which is apedal (massive) and has organic and
iron/aluminium concentrations (humosesquic). There is a clear change to a mottled brownish yellow (occasionally light grey) coarse sandy clay loam to sandy clay. This is weakly structured and acidic, often with very pale brown and dark reddish brown mottles and some quartz gravel. This soil grades into lighter textured weathered material or regolith. The profile depth is about 150 cm or more with variable depths of the surface horizons, generally 10-15 cm for the surface and 70 cm for the subsurface, often deeper. The pan is about 20-40 cm thick.

Notable features include:

• Gradational or limited (uniform) change in clay percentage with depth.
• There may be a mottled clayey base at depth (deep Sodosol).
• There may be occasional indurated or accumulation zones with in the predominantly coarse soil (Podosols).
• Despite neutral to slightly alkaline pH these soils have low nutrient capacity and low water holding capacity.
• These soils are susceptible to wind and sheet erosion, particularly on sloping terrain given weak consistence (strength)/low coherence and lighter textured surface materials.