SW79

Location: Yeo

Australian Soil Classification: Vertic, Mottled-Subnatric, Black SODOSOL
Great Soil Group: Solodic

General Landscape Description: Gently undulating rises.
Site Description: Crest of lower slope (2^o).
Geology: Mapped as Tertiary-Gellibrand Marl (Colac sheet 1:50 000) but most likely Hanson Plain Sand

SW79 Landscape

Soil Profile Morphology:

Surface Soil

Ap	0-20 cm	Very dark brown (10YR2/2 moist), gray (10YR5/1 dry); fine sandy loam; pH 5.1; clear change to:	SW79 Profile. Note: Surface (Ap) horizon has been stripped from the soil profile
A21e	20-40 cm	grayish brown (10YR5/2 moist), conspicuously bleached (10YR7/1 dry); fine sandy loam; pH 6.4; clear change to:
A22ec	40-50 cm	grayish brown (10YR5/2 moist), very pale brown (10YR8/2 dry); fine sandy loam; abundant rounded ironstone gravel (5-20 mm), minor fine quartz (8-20 mm); sharp change to:
Subsoil
B2t	50-90/110 cm	Very dark grayish brown (10YR3/2 moist) with few, fine (up to 20 mm) red mottles on ped interiors; medium heavy clay; strongly pedal, coarse to medium (40-60 mm) prismatic, parting to coarse (30-40 mm) blocky structure (with some fine lenticular peds); sandier matrix as horizon deepens; pH 6.6; abrupt to clear and irregular change to:
C	110 cm+	Yellow and gray mottled cemented sand with thick dark clay infills in cracks; infills can be quite thick (3 mm) and take form of vertical lenticular clay peds; pH 6.

• Strong texture contrast between surface (A) horizons and subsoil (B21) horizons.
• Large amount of iron stone gravel ("buckshot") in deeper subsurface (A22) horizon.

	pH	Salinity Rating	Sodicity	Dispersion
Surface (Ap horizon)	Strongly Acid	Medium	Non-Sodic	None
Subsoil (B21 horizon)	Slightly Acid	Very Low	Marginally Sodic	None

The surface soil is strongly acid. The subsoil is slightly acid.

Salinity rating is medium in the surface becoming very low in the subsoil.

The soil is non sodic in the surface and marginally sodic in the subsoil.

The clay content increases markedly at the A/B boundary.

Horizon	Horizon Depth (cm)	pH (water)	pH (CaCl2)	EC 1:5	NaCl %	Exchangeable Cations
						Ca	Mg	K	Na
						meq/100g
Ap	0-10	5.1	4.5	0.32	0.03	3.5	0.8	0.7	<0.1
A2	25-40	6.4	5.4	<0.05		0.99	0.97	0.07	0.17
B2	60-80	6.6	6.1	0.15		4.4	8.5	0.19	1.5
C	130+	6.8	6	0.11	0.02

Horizon	Horizon Depth (cm)	Exchangeable Aluminium mg/kg	Exchangeable Acidity meq/100g	Organic Carbon %	Nitrogen %	Field Capacity pF2.5	Wilting Point pF4.2	Coarse Sand (0.2- 2.0 mm)	Fine Sand (0.02- 0.2 mm)	Silt (0.002- 0.02 mm)	Clay (<0.002 mm)
Ap	0-10	24	16	4.9	0.42	26.2	10.9	21	45	15	8
A2	25-40	<10	4.4			15	3.5	19	54	17	10
B2	60-80		12			42.3	30.1	3	8	4	85
C	130+

Management Considerations:

Subsoil (B) Horizons

• The subsoil displays vertic features (i.e. slickensides) which indicates that significant shrinking and swelling occurs during wetting and drying cycles. This may have engineering implications and is likely to explain the variability in surface horizon depth across the trench.

• As the B horizon approaches C horizon peds gradually become sandier in the matrix until subsoil takes on the appearance of a fractured sandstone with thick clay coatings infilling in the cracks. These in places are quite thick (~3 mm) and take on form of vertical lenticular peds.
• Soil approx. 1 m over weathered sandstone probably Tpb but mapped as Tmi on 1:50 000 Beech Forest geology sheet. Boundary to B horizon becomes extremely wavy (30-80 cm depth) as unit continues down slope. Abundant gravel in A2, 100 to 400 mm thickness.