Soil/Landform Unit 122

Landform Unit Description

The gently undulating plains include the township of Cobden (looking at the western end of Cobden towards Ewen Hill)

Area:

5050 ha

0.38% of CMA region

Basaltic plains running from Cobden to Glenfyne are characterised by long gentle slopes with stringybarks (

E. obliqua

and

E. baxteri

) and swamp gums (

E. ovata

). The gently undulating plains of the Western Plains are bounded by a steep scarp to the east defining the margin with the entrenched valley of the Curdies River. This dissection has produced magnificent dissected terrain highlighting a wide diversity of geologies and vegetation types. Owing to the mix of geologies on the plains (

Quaternary

basalt and Neogene fluvio-marine sand), there is a wide range of soils. The major soils are sporadically

bleached

mottled

texture contrast soils with some upper slopes and crests having a few surface stones that are easily cleared. Upper slopes and crests are known to have shallow

friable

gradational soils associated with these stones. There are minor occurrences of texture contrast soils on the slopes, with relatively poorly drained equivalents on the flats. Grey cracking clays are found in depressions and drainage lines.

Gilgai

patches occur on these plains with the texture contrast soils common on both mounds and depressions.

Buckshot

in surface horizons is higher in depressions compared to mounds. Land use is quite diverse and includes dairy farming, beef cattle and sheep grazing, water supply, softwood plantation and residential development (especially around Cobden). Erosion hazards are minimal except at scarps, which have a high susceptibility to mass movement. Areas with shallow stony gradational soils are susceptible to

leaching

of nutrients, and compaction is a problem on the flatter gilgaied areas.

Grassed gently undulating plains are used for grazing (sheep, beef and dairy cattle)
	Grassed plains, most large vegetation has been removed and replaced with annual/perennial pastures

Component	1	2	3	4	5
Proportion of soil-landform unit	14%	6%	45%	30%	5%
CLIMATE Rainfall (mm)	Annual: 860
Temperature (^oC)	Minimum 9, Maximum 18
Precipitation less than potential evapotranspiration	November-March
GEOLOGY Age and lithology	Quaternary basalt, Neogene fluvio-marine sand
Geomorphology	6.1.3 Volcanic Western Plains with poorly developed drainage
LANDUSE	Uncleared: Nature conservation; water supply Cleared: Dairy farming; beef cattle and sheep grazing; water supply; softwood plantation
TOPOGRAPHY Landscape	Gently undulating basalt plains
Elevation range (m)	61-149
Local relief (m)	2-5
Drainage pattern	Dendritic
Drainage density (km/km²)	0.8
Landform	Low rises			Plains	Drainage depressions
Landform element	Broad low crests and upper slopes	Mid slopes	Long gentle lower slopes	Flats	Swamps and depressions
Slope and range (%)	3 (1-5)	6 (3-10)	2 (1-5)	1 (0-3)	2 (1-5)
Slope shape	Convex	Irregular	Concave	Straight	Concave
NATIVE VEGETATION Ecological Vegetation Class	Herb-rich Foothill Forest (2.3%), Plains Grassy Woodland (1.4%)
SOIL Parent material	Basalt	Basalt	Basalt and colluvium	Basalt	Alluvial sand, silt and clay and basaltic colluvium
Description (Corangamite Soil Group)	Acidic and neutral mottled brown, grey or yellow texture contrast soils (37)	Acidic and neutral mottled brown, grey or yellow texture contrast soils (37) and minor shallow friable loams (41)	Acidic and neutral mottled brown, grey or yellow texture contrast soils (37)	Acidic and neutral mottled brown, grey or yellow texture contrast soils (37)	Acidic mottled black texture contrast soils and grey cracking clays (31)
Soil type sites	MM232, SFS5b, SW48	SFS5b, SW48, SW8	MM232, SFS5b, SW48	MM232	SW37, CLRA48, CLRA15
Surface texture	Fine sandy clay loam	Fine sandy clay loam	Fine sandy clay loam	Clay loam	Fine sandy clay loam, light medium clay
Permeability	Low to moderate	Low to moderate	Low	Low	Low to very low
Depth (m)	<2	<2	>2	>2	>2
LAND CHARACTERISTICS, POTENTIAL AND LIMITATIONS	Texture contrast soil, moderate water holding capacity and moderate nutrient holding capacity in surface and subsurface soils, higher in deep subsoil. Low to very low permeability. Stony. Non-sodic subsoil. Moderate site drainage.	Texture contrast soil, moderate water holding capacity and moderate nutrient holding capacity in surface and subsurface soils, higher in deep subsoil. Low to high permeability (friable loams). Some stone. Non-sodic subsoil. Moderately rapid site drainage.	Texture contrast soil, moderate water holding capacity and moderate nutrient holding capacity in surface and subsurface soils, higher in deep subsoil. Low permeability. Some stone. Non-sodic subsoil. Moderate to slow site drainage. Possible compaction.	Texture contrast soil, moderate water holding capacity and moderate nutrient holding capacity in surface and subsurface soils, higher in subsoil. Low permeability. Some stone. Non-sodic subsoil. Moderate to slow site drainage. Possible compaction.	Uniform firm texture and texture contrast, expansive clays, high water holding capacity and nutrient holding capacity. Strongly sodic subsoil, possible surface soil associated with poor drainage. Some friable self-mulching surfaces with high organic matter. Very slow site drainage.

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