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SW90

Location: Mount Pollock

Australian Soil Classification: Calcic, Mottled-Mesonatric, Black SODOSOL

General Landscape Description: Undulating low hills/rolling low hills.
Site Description: Simple slope.
Geology: Quaternary-Newer Volcanics.

Image: SW90 Landscape
SW90 Landscape


Soil Profile Morphology:


Surface Soil


A10-15 cmVery dark grey (10YR3/1 moist); fine sandy loam; pH 5.5:
Image: SW90 Profile
SW90 Profile - Note: Surface (A1) horizon has been stripped from soil profile.
A215-25 cmDark greyish brown (10YR4/2 moist), light brownish grey (10YR6/2 dry); fine sandy loam; weakly pedal; common fine buckshot; pH 6.2; sharp change (thin discontinuous bleached contact) to:
Subsoil
B21t25-60/70 cmVery dark grey (10YR3/1 moist); heavy clay; few small yellowish brown (10YR5/8 moist) mottling; very coarse (200 mm) prismatic to columnar (200 mm), parting to coarse prismatic and blocky structure; strong consistence dry; pH 6.6; abrupt boundary to:
B22g60/70+ cmDark greyish brown (10YR4/2 moist) with common (~20%), diffuse, yellowish brown (10YR5/4-5/6 moist) mottles; heavy clay; apedal; common amount of buckshot; large irregular rounded basalt boulders (>60 cm) at unusual angles (possibly colluvial); pH 8.5.

Key Profile Features:
  • Strong texture contrast between surface (A) horizons and subsoil (B21) horizon.
  • Very coarse prismatic to columnar structure in upper subsoil.

Soil Profile Characteristics:

pH
Salinity Rating
Surface
(A1 horizon)
Strongly Acid
Low
Non Sodic
None
Subsoil
(B21 horizon)
Slightly Acid
Low
Strongly Sodic
Complete
Deeper Subsoil
(at 75-90 cm)
Moderately Alkaline
Low - Moderate
Strongly Sodic
Complete


Image: SW90 Graphs

The surface is strongly acid. The subsoil is slightly acid becoming moderately alkaline at depth.Salinity rating is low in the surface and upper subsoil becoming low to moderate in the deeper subsoil.The soil is non sodic in the surface and strongly sodic in the subsoil.The clay content increases markedly at the A/B boundary.


Horizon
Sample Depth
(cm)
pH
(water)
pH
(CaCl2)
EC
1:5
NaCl
%
Exchangeable Cations
Ca
Mg
K
Na
meq/100g
A1
0-5
5.5
4.7
0.14
3.4
3
0.5
0.59
A2
15-25
6.2
5.1
0.1
3
3.3
0.21
1.1
B21t
30-50
6.6
5.5
0.19
4.3
10
0.47
3.6
B22g
75-90
8.5
7.4
0.32
0.03
3.8
9.7
0.3
5.2
120+
8.6
7.4
0.22
0.03

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
0-5
<10
11
3.6
0.27
26.6
9.7
25
38
17
14
A2
15-25
<10
6.1
22.7
7.2
25
39
17
16
B21t
30-50
40.2
19.6
18
27
11
39
B22g
75-90
35.9
16.2
21
32
11
32
120+


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.
  • The dense and coarsely structured subsoil is strongly sodic and disperses completely in water. This will result in restricted root and water movement into the subsoil.

Profile Described By: Richard McEwan (March1999).
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