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What is grey clay?
What do grey clay soils look like?
Hardsetting grey clays are commonly know as 'grey clay' or 'Sunday soils', however they are also called 'Moort soils' or 'Mongrel soils'. These names are used to describe several soil types. In the Great Southern Agricultural Region there are 5 different soils types that are referred to as grey clay.
Despite different names and some different properties, the management of the five soil types is essentially the same because of their common properties. They all have:
- A hardsetting surface
- Shallow topsoil (less than 15 cm in depth and often less than 10 cm),
- A very dense, compact subsoil,
- A sodic or dispersive soil profile creating poor infiltration, aeration and drainage, and;
Limited amounts of plant available water.
Some grey clay soils will also crack deeply when dry, as this picture illustrates
A typical grey clay soil profile with shallow topsoil and dense subsoil.
Surface water ponding on grey clay seedbeds illustrates poor infiltration and often causes poor crop establishment.
The pH of grey clay topsoil varies. It can be acidic, but the subsoil is always alkaline. Grey clay soils with a higher clay content will crack deeply when dry. An example of this soil type can be found at Wemyss Estate in Mindarabin, Western Australia.
What is their natural vegetation?
The species most associated with hardsetting grey clay is the Moort tree (Eucalyptus platypus) which is well adapted to growing in the conditions imposed by grey clay soils. Many farmers believe the Moort tree is an indicator of the presence of grey clay soils.
The Moort tree was given the scientific name of Eucalyptus platypus, as the distinctive flower buds of the tree look like the claw of a platypus.
However, the Moort tree is not found exclusively on "Moort soil" and neither is it the only form of native vegetation to grow successfully on hardsetting grey clay. Other species are:
- wandoo (Eucalyptus wandoo),
- York gum (E. loxophleba),
- red morrell (E. longicornis),
- flat-topped yate (E. occidentalis),
- salmon gum (E. salmonphloia)
- small mallees (Eucalyptus spp.)
- rock sheoak (Allocasuarina huegeliana), and;
- jam (Acacia acuminata).
Where are they found in the landscape?
Hardsetting grey clay soils occupy 1.5 million hectares in the central and southern wheatbelt of Western Australia. Grey clay soils occupy 15% of the soils in the Great Southern Agricultural region. Generally, they are located in valley flats, alluvial plains and lower to mid slopes. Sometimes it is distributed on slopes of rises or crests.
Grey Clays Research Officer,
Phone: 08 9821 3236