The self mulching clays have a uniform heavy clay texture from the
surface to deep into the soil profile. The surface soil, when dry, is self
mulching, being composed of easily disturbed small aggregates
resulting from extensive swelling and shrinking from wetting and
drying.
These soils are found in gilgai formations, usually in association
with transitional red brown earths. The self-mulching clay soils occur
as the mound or puff in gilgai formations, while in the lower areas
between the mounds transitional red brown earths are usually found.
The proportion of the mound compared with the shelf in gilgais varies.
The proportion of the mound in a gilgai formation therefore influences
the land-use options and management of a particular area. Areas with
more than 50% mound as a proportion of the total area are usually
considered to be self-mulching soils.