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SW8

Location: Alvie

Australian Soil Classification: Sodic, Eutrophic, Brown DERMOSOL

General Landscape Description: Lower slope of a gently undulating rise.
Geology: Quaternary volcanic ash deposits (Qvs).
Land Use: Pasture has been cultivated and improved. Alternate with silage crop. Irrigated in Summer.

SW8 Landscape
SW8 Landscape

Soil Profile Morphology:

Surface Soil

A10-15 cmBrown (7.5YR4/2); firm surface condition; fine sandy clay loam; moderate medium blocky, parting to moderate fine blocky structure; firm consistence moderately moist; pH 6.6; clear change to:
SW8 Profile
SW8 Profile
Subsoil

B2115-25 cmDark reddish brown (5YR3/3); heavy clay loam (becoming light clay with depth); moderate medium blocky, parting to moderate fine polyhedral structure; firm consistence moderately moist; pH 6.5; abrupt change to:
B2225-40 cmDark brown (7.5YR3/4); light medium clay; strong medium polyhedral, parting to strong fine polyhedral structure, smooth faced peds; very firm consistence dry; pH 6.5; gradual change to:
B2340-50 cmDark brown (7.5YR3/2); medium clay; strong coarse blocky, parting to strong fine polyhedral structure; firm consistence slightly moist; roots to 50cm; pH 7.1; gradual change to:
B/C50-70 cmDark brown (7.5YR3/2); fine sandy clay loam; very firm to strong consistence dry; contains a common (20%) amount of weathered basalt and volcanic ash; pH 8.0:
C70+ cm Volcanic ash deposits.

Key Profile Features:
  • Lack of strong texture contrast between surface (A) horizons and subsoil (B21) horizon.
  • Moderately deep soil profile (ie. 70 cm) overlying volcanic ash deposits.

Soil Profile Characteristics:




pH



Salinity Rating
Surface
(A1 horizon)
Slightly Acid
Low
Sodic
None
Subsoil
(B21 horizon)
Slightly Acid
Very Low
Marginally Sodic
None
Deeper Subsoil
(at 50-70 cm)
Moderately Alkaline
Moderate
Non-Sodic
None


SW8 graphs

The surface (A) horizons and upper subsoil are slightly acid. The deeper subsoil is slightly alkaline becoming moderately alkaline at depth.
      The salinity rating is low to very low becoming moderate at depth.
    The surface is sodic. The upper subsoil (15-25 cm depth) is only marginally sodic. Strong dispersion occurs after remoulding. The deeper subsoil is non-sodic and dispersion occurs after remoulding.
    The clay percentage increases gradually down the profile but decreases in the B/C horizon when ash is mixed in.

Horizon
Horizon Depth
(cm)
pH
(water)
pH
(CaCl2)
EC
1:5
Exchangeable Cations
Ca
Mg
K
Na
meq/100g
A1
0-15
6.6
5.6
0.14
7.3
7.7
0.71
1.3
B21
15-25
6.5
5.5
0.11
6.4
10
0.68
0.95
B22
25-40
6.5
5.5
0.09
7.4
19
0.85
1.1
B23
40-50
7.1
5.9
0.08
8.2
28
0.89
1.1
B/C
50-70
8.0
7.2
0.22
11
26
0.83
1.7



Horizon
Horizon Depth
(cm)
Organic Carbon
%
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
0-15
2.4
16.1
7.0
34.8
21.0
30.0
B21
15-25
1.4
17.9
7.0
31.5
14.5
41.0
B22
25-40
24.6
6.7
21.8
11.0
53.5
B23
40-50
30.5
6.3
18.4
10.5
57.0
B/C
50-70
23.7
23.4
36.0
14.0
17.5


Management Considerations:

Whole Profile

  • Plant available water capacity (PAWC) is considered to be low (estimated at 85 mm) for this soil profile. This is based on available laboratory data. Effective rooting depth will be restricted by the compacted ash deposits in the deeper subsoil. Most roots in the soil pit were observed to 50 cm depth.
Surface (A) Horizons
  • The inherent fertility (based on the sum of the exchangeable basic cations) of the surface horizons is moderate-high.
  • The surface soil is reasonably well structured (parting to fine blocky structure) which should allow for good root proliferation.
  • Due to the relatively high clay content in the surface horizon, such soils may be prone to compaction if excessively disturbed (eg. cultivation, trafficking) whilst in a moist-wet condition (ie wetter than the plastic limit).
Subsoil (B) Horizons
  • Although non-sodic, the upper subsoil disperses slightly (strongly after remoulding). Disturbance to this horizon by deep tillage (when in a moist to wet condition) may result in some structural degradation occurring.
  • Exchangeable magnesium levels are high in the subsoil horizons (ie. > 45%). Values of exchangeable magnesium to Cation Exchange Capacity of over 20 % can induce potassium deficiency in some soils (Baker et al. 1993).

Profile Described By: Mark Imhof, Austin Brown, Paul Rampant, Graeme Ward and Ruth Lourey (April 1996).
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