Victorian Resources Online (archived)

SW103

Location: Lara

Australian Soil Classification: Epicalcareous - Epihypersodic, Massive, Red VERTOSOL (moderate profile depth)

General Landscape Description: Near level plain.
Site Description: Broad flat ridge with easterly aspect slope <1%.
Geology: Quaternary Basalt.

Soil Profile Morphology:

Surface Soil

Ap	0-12 cm	Brown (7.5YR4/3 moist); hardsetting surface condition; light clay; apedal structure; contains shelly material including intact shells; pH 7.9; clear and smooth change to:	SW103 Profile - Note: Surface stripped from soil profile.
Subsoil
B21t	12-30 cm	Dark reddish brown (5YR3/3 moist); medium heavy clay; fine prismatic structure, parting to fine polyhedral; pH 9; clear and smooth change to:
B22ss	30-60/75 cm	Dusky red (2.5YR3/3), becoming brown (7.5YR4/3) at depth; medium heavy clay; prominent slickensides (up to 30 cm across); pH 9.5; clear and wavy change to:
B23k	60/75-80/100 cm	Reddish yellow (7.5YR6/8) becoming reddish yellow (7.5YR7/8) at depth; abundant soft calcium carbonate (CaCO₃); irregular change to:
C	80/100+ cm	Weathering vesicular soft greenish basalt; tongues of calcium carbonate (CaCO₃) from B23k above; some biological activity present (ant nests).

Key Profile Features:

High (>35%) clay content throughout the soil profile.
Massive (hardsetting) surface horizon.
Vertic features (slickensides) in subsoil.
Calcium carbonate segregations in deeper subsoil.
Moderate soil profle depth – overlying weathering fractured basalt.

Soil Profile Characteristics:

	pH	Salinity Rating	Sodicity	Dispersion
Surface (A1 horizon)	Slightly Alkaline	Low	Non-Sodic	None¹
Subsoil (B21 horizon)	Strongly Alakaline	Low	Strongly Sodic	Moderate-Strong
Deeper Subsoil (at 40-55 cm)	Very Strongly Alkaline	Medium-High	Strongly Sodic	Strong-Complete
¹ Strong dispersion after remoulding.

The surface is slightly alkaline. The subsoil is strongly alkaline becoming very strongly alkaline at depth.

Salinity rating is low in the surface and upper subsoil becoming medium to high at depth.

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

The clay content is high throughout the profile.

Horizon	Sample Depth (cm)	pH (water)	pH (CaCl₂)	EC 1:5	NaCl %	Exchangeable Cations
						Ca	Mg	K	Na
						meq/100g
A1	0-10	7.9	7.3	0.2		21	4.1	1.5	0.8
B21	15-30	9	8	0.42	0.02	15	8.8	1.4	7
B22	40-55	9.5	8.8	0.73	0.04	7.7	16	1.9	12

Horizon	Sample Depth (cm)	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	2.3	0.26	33.1	18.4	12	21	17	42
B21	15-30			55.3	29.6	5	14	11	65
B22	40-55			63.7	35.3	4	14	17	58

Management Considerations:

Whole Profile

The relatively high wilting point (i.e. 18%) indicates that plants will be unable to fully utilise light rains when the soil is dry.
Tillage of cracking clay soils should be avoided if the soil is wet (i.e. wetter than the plastic limit). At such moisture conditions, excessive tillage, trafficking or over stocking could result in structural damage (i.e. compaction, smearing) occurring. Ideally tillage and trafficking should take place when the soil is drier than the plastic limit.

Profile Described By: Richard McEwan (February 1999).

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