Soil/Landform Unit 175

Gently undulating plains near Irrewillipe

Area:

8524 ha

0.6 % of CMA region

This unit forms an apron of sediments (mainly Neogene) from Colac west to Pirron Yallock, with components of broad low crests, slopes and plains. As a member of the sedimentary Western Plains, the unit is bound by stony rises (Units

) and

to the north, and

flats (Unit

) and undulating sedimentary rises (Unit

170

) to the south. Native vegetation classes of the unit include Grassy Woodland and Plains Grassy Woodland. The soils are sodic,

mottled

black texture contrast soils (

Sodosols

) that are susceptible to waterlogging on the plains and drainage lines. Rainfall is sufficient to sustain intensive grazing (dairying) and other uses such as plantations or woodlots. Excavation of peats is also undertaken on these gently undulating plains. Susceptibility to nutrient decline and minor sheet erosion particularly applies to the slopes. Increasing

sodicity

may be a problem in the lower landscape positions.

The level plains near Bungador are especially prone to seasonal waterlogging
	The level plains near Warncoort are mainly used for grazing and cropping

Component	1	2	3	4	5
Proportion of soil-landform unit	7%	20%	30%	40%	3%
CLIMATE Rainfall (mm)	Annual: 810
Temperature (^oC)	Minimum 8, Maximum 19
Precipitation less than potential evapotranspiration	November–March
GEOLOGY Age and lithology	Neogene fluvial and marine sediments, Recent clay, sand and gravel and minor basalt
Geomorphology	6.2.4 Plains, rises and low hills of the Sedimentary Western Plains
LANDUSE	Uncleared: Nature conservation; water supply Cleared: Dairy farming; beef cattle and sheep grazing; cropping (wide range of cereals); horticulture
TOPOGRAPHY Landscape	Gently undulating plains
Elevation range (m)	114–168
Local relief (m)	20
Drainage pattern	Centripetal–parallel
Drainage density (km/km²)	0.6
Landform	Gentle slopes			Plains	Drainage lines
Landform element	Broad low crests	Mid and upper slopes	Lower slopes	Plain	Drainage depressions
Slope and range (%)	4 (1–7)	5 (3–12)	3 (2–5)	1 (0–3)	2 (1–3)
Slope shape	Convex	Convex	Convex	Straight	Concave
NATIVE VEGETATION Ecological Vegetation Class	Grassy Woodland (0.4%), Plains Grassy Woodland (0.3%)
SOIL Parent material	Sand, silt and clay	Sand, silt and clay	Sand, silt and clay	Sand, silt and clay	Alluvial sand, silt and clay
Description (Corangamite Soil Group)	Neutral mottled black texture contrast soils (14)	Neutral mottled black texture contrast soils (14)	Acidic and neutral mottled black texture contrast soils (14)	Acidic and neutral mottled black texture contrast soils (14)	Black cracking clays (32) and neutral mottled black texture contrast soils (31)
Soil type sites	SW99, SW93, MM204	SW99, SW93, MM363	SW99, SW93, MM204	SW99, SW93, MM204	SW88, SW95, SW37
Surface texture	Loam, fine sandy	Loam, fine sandy	Loam, fine sandy	Loam, fine sandy	Light clay; loam, fine sandy
Permeability	Moderate	Low to moderate	Low	Low	Very low
Depth (m)	<2	<2	<2	>2	>2
LAND CHARACTERISTICS, POTENTIAL AND LIMITATIONS	Texture contrast, low to moderate water holding capacity and nutrient holding capacity depending on depth and stoniness in upper soil, high in subsoil. Non-sodic (moderate structure) and sodic (coarse structure) subsoils. Moderate site drainage. Some susceptibility to nutrient decline and sheet and rill erosion.	Texture contrast, low to moderate water holding capacity and nutrient holding capacity depending on depth and stoniness in upper soil, high in subsoil. Non-sodic (moderate structure) and sodic (coarse structure) subsoils. Moderate site drainage. Some susceptibility to nutrient decline and sheet and rill erosion.	Texture contrast, low to moderate water holding capacity and nutrient holding capacity depending on depth and stoniness in upper soil, high in subsoil. Non-sodic (moderate structure) and sodic (coarse structure) subsoils. Moderate to slow site drainage. Some susceptibility to nutrient decline, sheet and rill erosion.	Texture contrast, low to moderate water holding capacity and nutrient holding capacity depending on depth and stoniness in upper soil, high in subsoil. Non-sodic (moderate structure) and sodic (coarse structure) subsoils. Slow site drainage. Some susceptibility to nutrient decline and sheet and rill erosion.	Texture contrast and expansive clays, low to high water holding capacity and nutrient holding capacity depending on depth in upper soil, high in subsoil. Non-sodic (moderate structure) and sodic (coarse structure) subsoils. Very slow site drainage. Some susceptibility to waterlogging and nutrient decline.

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