Victorian Resources Online (archived)

SW83

Location: Warncoort

Australian Soil Classification: Vertic (& Calcic ), Subnatric, Black SODOSOL

General Landscape Description: Gently undulating plain.
Site Description: Trough of a gilgai.
Geology: Basalt plain.

Soil Profile Morphology:

Surface Soil

A1	0-10 cm	Very dark brown (10YR2/2 moist); loam; pH 5.5; clear change to:	SW83 Profile. Note: Surface (A1) horizon has been stripped from the profile
A2	10-60 cm	Dark grayish brown (10YR4/2 moist) conspicuously bleached (10YR7/2 dry); sandy clay loam; apedal; massive; few (2%), fine buckshot nodules (concentrated in pockets); firm consistence dry; pH 6.6; abrupt and wavy change to:
Subsoil
B21	60-90 cm	Black (10YR2/1 moist); heavy clay; few pockets of ferruginous fine gravel; coarse prismatic structure; pH 6.8; abrupt change to:
B22	90+ cm	Gray (10YR6/1 moist) with very few (<2%) brownish yellow (10YR6/8 moist) and dark red (2.5YR4/8 moist) mottles; medium clay; medium prismatic structure; strongly vertic; soft calcareous segregations; pH 8.6.

Key Profile Features:

Strong texture contrast between surface (A) horizons and subsoil (B) horizons.
Variable depth of A horizons due to gilgai microrelief.

Soil Profile Characteristics:

	pH	Salinity Rating	Sodicity	Dispersion
Surface (A1 horizon)	Strongly Acid	Low	Non-Sodic	None
Subsoil (B21 horizon)	Slight Acid	Very Low	Sodic	None¹
Deeper Subsoil (at 90+ cm)	Strongly Alkaline	Low	Strongly Sodic	Strong - Complete
¹ Complete dispersion after remoulding.

The surface soil is strongly acid. The subsoil is slightly acid becoming strongly alkaline with depth.

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

The soil is non sodic in the surface. The upper subsoil is sodic becoming strongly sodic in the deeper subsoil.

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

Horizon	Sample Depth (cm)	pH (water)	pH (CaCl₂)	EC 1:5	Exchangeable Cations
					Ca	Mg	K	Na
					meq/100g
A1	0-10	5.5	4.9	0.21	6.2	3.2	0.61	0.37
A2	10-60	6.6	6	0.06	1.7	1.4	<0.05	0.18
B21	60-90	6.8	5.6	0.11	5.9	11	0.3	2.4
B22	90+	8.6	7.5	0.25	7	12	0.28	4

Horizon	Sample 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)


A1	0-10	<10	12	3.8	0.29	25.6	10.8	23	37	14	21
A2	10-60		3.3			16.6	3.8	29	46	14	12
B21	60-90		11			39.4	22.4	14	21	7	55
B22	90+					39.3	19.9	15	28	8	47

Management Considerations:

Subsoil (B) Horizons

This profile is the “hollow” of a gilgai soil. See GP 82 for description of the associated “puff”.
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.

Notes

Very variable between puffs and hollows. Intermittent/discontinuous cycle is every 2 - 3 m.

Profile Described By: Richard McEwan (March 1999).

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