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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 cmVery dark brown (10YR2/2 moist); loam; pH 5.5; clear change to:
South West Gasp Pipeline SW83 Profile
SW83 Profile. Note: Surface (A1) horizon has been stripped from the profile
A210-60 cmDark 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
B2160-90 cmBlack (10YR2/1 moist); heavy clay; few pockets of ferruginous fine gravel; coarse prismatic structure; pH 6.8; abrupt change to:
B2290+ cmGray (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
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.



Image: SW83 Graphs

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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