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SW86

Australian Soil Classification: Vertic (& Calcic), Mottled-Mesonatric, Black SODOSOLGeneral Landscape Description: Gently undulating basalt plain
Site Description: Depression, flatGeology: Quaternary-Newer Volcanics


Soil Profile Morphology:


Surface Soil


Ap0-8 cmVery dark brown (10YR2/2 moist), greyish brown (10YR5/2 dry); sandy clay loam; rusty root channel mottling prominent; hard-setting; strong consistence; pH 6.2; clear change to:
South West Gasp Pipeline GP86 Profile
SW86 Profile
A28-17 cmVery dark greyish brown (10YR3/2 moist and 10YR5/1 dry); loam; rusty mottling prominent (~5% fine magnetic buckshot); strong consistence; pH 6.9; abrupt change to:
Subsoil
B21tg17-40 cmVery dark greyish brown (10YR3/2 moist), dark greyish brown (10YR4/2 dry) with olive grey (5Y5/2 moist) mottles in ped interiors, and prominent yellowish brown (10YR5/8 moist) mottles associated with root channels; light medium clay to medium clay; many (~25%); roughly coarse prismatic (~100 mm), parting to coarse (mostly rough-face) blocky and angular coarse blocky; very strong consistence, pH 8.1; clear change to:
B22ss40-60 cmVery dark greyish brown (2.5Y3/2 moist); fine lenticular and polyhedral structure; moderate slickensides; pH 8.6; clear change to:
B2380-200 cmOlive to light olive grey (5Y6/2-5/3 moist); fine brownish yellow (10YR6/8 moist) mottles; soft, yellowish white carbonate; calcareous continues to 2 metres; pH 9.2.


South West Gasp Pipeline GP86 Slickensides
Slickensides in B22ss horizon (40-60 cm)

Key Profile Features:

  • Strong texture contrast between surface (A) horizons and subsoil (B21) horizon.

Soil Profile Characteristics:

pH
Salinity Rating
Sodicity
Dispersion
Surface
(A1 horizon)
Slightly Acid
Low
Non-Sodic
None1
Subsoil
(B21 horizon)
Moderately Alkaline
Medium - High
Strongly Sodic
Strong
Deeper subsoil
(at 80 cm)
Very Strongly Alkaline
High - Very High
Strongly Sodic
-
1 Moderate dispersion after remoulding

South West Gasp Pipeline GP86 Graphs

Horizon
Horizon Depth
(cm)
pH
(water)
pH
(CaCl2)
EC
1:5
NaCl
%
Exchangeable Cations
Ca
Mg
K
Na
meq/100g
A1
0-8
6.2
5.7
0.24
7.3
8.9
0.72
1.4
A2
8-17
6.9
6.2
0.15
4
5.2
0.2
1
B21
17-40
8.1
7.3
0.6
0.11
4.4
12
0.7
3.8
B22
40-60
8.6
8.1
1.6
0.4
5.1
18
0.8
7.5
B23
60-80
8.8
8.5
2
0.46
5
19
0.7
8.1
B24kg
80-200
9.2
8.6
1.3
0.25

Horizon
Horizon Depth
(cm)
Ex Al
mg/kg
Ex Ac
meq/100g
Field
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
0-8
<10
12
35
17.9
20.2
30.5
14
28
A2
8-17
22.2
8.9
26.1
39.6
15
18
B21
17-40
38.7
18.2
15.1
31.8
12.5
37
B22
40-60
46.6
24.9
11.6
24.4
13
47.5
B23
60-80
B24kg
80-200


Management Considerations:

Subsoil (B) Horizons

  • The dense and coarsely structured subsoil is sodic and disperses completely. This will result in significantly restricted root and water movement into the subsoil.
  • 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.
  • The subsoil has a high level of soluble salts, which will restrict the growth of salt-sensitive species.

Notes
  • To the west rising out of the depression more rock is present but soil deeper than west of GP 16. Cracking content at the surface which is rough and hard setting. Sea Barley grass and thistles. Heavy prismatic structures greyer than previous site.


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