Soil/Landform Unit 93

Rolling plains from Robinsons Road near Barongarook

Area:

7745 ha

0.58% of CMA region

North of Forrest and extending towards Colac, undulating plains with often deeply weathered soils are found. The geology is mainly

Pliocene

clay with minor outcrops of sand. Redistribution of surface sand has resulted in polygenetic soils over much of the landscape, with weak hardpan development and impeded drainage. Surface soils seem to be naturally low in plant nutrients. Many areas remain uncleared and support open forests dominated by

Eucalyptus obliqua

and

E. radiata

E. baxteri

is notably absent in this slightly drier region. Other areas have been cleared for agriculture or converted to pine plantations. The main hazards to land use are loss of soil structure by

compaction

and leaching of nutrients.

Cultivated crest and upper slope overlooing lower slopes and plains
	Poor site drainage and low soil permeability lead to waterlogging and pugging of the soil by stock

Component	1	2	3	4	5
Proportion of soil-landform unit	8%	55%	15%	15%	7%
CLIMATE Rainfall (mm)	Annual: 700-900, lowest January (40), highest August (80)
Temperature (^oC)	Annual: 13, lowest July (8), highest February (18)
Seasonal growth limitations	Temperature: less than 10^oC (av.) June-August Precipitation: less than potential evapotranspiration late October-early April
GEOLOGY Age and lithology	Pliocene unconsolidated clay, silt and sand. Recent sand veneer
Geomorphology	3.3.2 Dissected rolling low hills of the Southern Uplands
LANDUSE	Cleared areas: Sheep and beef cattle grazing dairy farming Uncleared areas: Hardwood forestry for sawlogs, post and poles; nature conservation; active and passive recreation; softwood forestry, forest grazing
TOPOGRAPHY Landscape	Gently undulating to rolling plain in the western parts of the Barwon catchment
Elevation range (m)	120-280
Local relief (m)	30
Drainage pattern	Dendritic
Drainage density (km/km²)	1.2
Landform	Undulating plains
Landform element	Steep slope	Crest, upper slope	Upper and middle slope	Lower slope	Drainage line
Slope and range (%)	25 (15-40)	15 (0-10)	5 (0-10)	7 (1-15)	1 (0-2)
Slope shape	Linear	Convex	Convex	Linear	Concave
NATIVE VEGETATION Structure	Open forest	Open forest	Open forest	Woodland	Woodland
Dominant species	E. obliqua, E. radiata, E. viminalis	E. obliqua, E. radiata, occasionally E. ovata, E. viminalis	E. radiata, E. obliqua, E. nitida	E. radiata, E. nitida	E. ovata, E. radiata, occasionally E. aromaphloia
SOIL Parent material	Clay, silt and sand	Clay, silt and sand	Clay, silt and sand with quartz sand veneer	Clay, silt and sand with quartz sand veneer	Alluvium
Description (Corangamite Soil Group)	Brown, grey or yellow gradational soils, weak structure (17, 29)	Mottled brown. grey, yellow and red gradational soils (17, 21)	Grey sand soils, structured clay underlay (8)	Grey sand soils, weakly structured clay underlay (8)	Mottled brown, grey or yellow gradational soils (34)
Soil type sites	OTR497, OTR741	SW31, OTR746, OTR741	OTR737	- (OTR742)	- (OTR739)
Surface texture	Sandy loam	Loam	Sandy loam	Sandy loam	Loam
Permeability	High	Moderate	Low	Low	Moderate
Depth (m)	>2	>2	>2	>2	>2
LAND CHARACTERISTICS, POTENTIAL AND LIMITATIONS	Steeper slopes with weak structured surfaces are prone to sheet erosion.	Low inherent fertility and phosphorus fixation lead to nutrient decline.	Low inherent fertility with leaching of permeable surface horizons leads to nutrient decline.	Low permeability and seasonal perched watertable lead to waterlogging and soil compaction.	High seasonal watertable leads to waterlogging and soil compaction.

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