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GP38

Location: Winnindoo.Australian Soil Classification: Vertic (and Magnesic), Subnatric, Brown SODOSOL.
Great Soil Group: Solodic.Geology: Pleistocene sediments.
General Landscape Description: Level plain. Mapping Unit: Stratford.
Site Description: Road reserve with red gum (E. tereticornis).

Photo: G38 Landscape
Site GP38 Landscape


Soil Profile Morphology:

Surface Soil

A1 0-17 cmDark greyish brown (10YR4/2); sandy loam; weak medium polyhedral, parting to weak fine polyhedral structure; firm consistence dry; pH 5.8:

Photo: Site G38 Profile
Site GP38 Profile
A2 17-20 cmPale brown (10YR6/3) with a yellowish brown (10YR5/8) mottles in patches; sandy loam; contains many (40%) ferruginous nodules (2-10 mm in size); pH 6.4; discontinuous change to:

Note:
Sometimes the A2 forms a hard capping on top of the B21 horizon.

Subsoil

B21 20-60cmYellowish brown (10YR5/6) with strong brown diffuse (7.5YR5/8) mottles; medium heavy clay; weak coarse prismatic, parting to moderate coarse blocky and medium polyhedral structure; strong consistence dry; pH 6.5:

B22 60-90 cmYellowish brown (10YR5/6) with diffuse reddish yellow (7.5YR6/8) and dark red (2.5YR4/8) mottles; moderate coarse prismatic, parting to coarse blocky structure; many slickensides; pH 7.3:

B2390+ cm Yellowish brown (10YR5/6) with reddish yellow (7.5YR6/8) mottles; many slickensides present; pH 7.1.

Key Profile Features:
  • Strong texture contrast between surface (A) horizon (17% clay) and sodic subsoil (B21) horizon (79% clay).
  • Accumulation of ironstone nodules in the subsurface horizon.
  • Vertic properties (i.e. significant shrink-swell characteristics) in deeper subsoil.

Soil Profile Characteristics:

Horizon
pH
Salinity Rating
Surface
(A1 horizon)
Moderately Acid
Low
-
None1
Subsoil
(B21 horizon)
Slightly Acid
Very Low
Sodic
None2
Deeper subsoil
(at 1 m)
Slightly Alkaline
Low
Extremely sodic
Strong2
1 Moderate dispersion after remoulding.
2 Complete dispersion after remoulding.


Graph: pH levels in Site G38




The surface is moderately acid. The
subsoil is slightly acid becoming
slightly alkaline at 60 cm.
Graph: Sodicity levels in Site G38


The upper subsoil is sodic; becoming
strongly sodic at depth.
Graph: Salinity levels in Site G38


The salinity rating is low throughout
the profile.
Graph: Clay% in Site G38


The clay content increases significantly
at the A/B horizon interface.

Horizon
Horizon Depth
(cm)
pH
(water)
pH
(CaCl2)
EC 1:5
NaCl
Exchangeable Cations
Ca
Mg
K
Na
meq/100g
A1
0-17
5.8
5
0.06
2.7
2
0.29
0.4
A2
17-20
6.4
5
<0.05
1.1
1.3
0.09
0.29
B21
20-60
6.5
5.1
<0.05
3
10
0.4
1.8
B22
60-90
7.3
6.3
0.24
1.6
32
0.2
12
B23
90+
7.1
6.3
0.28
0.06
1
9.9
0.15
13

Horizon
Horizon Depth
(cm)
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
0-17
8
20
41
17
17
A2
17-20
5
30
39
17
3
B21
20-60
28
5
8
2
79
B22
60-90
31
3
5
1
83
B23
90+
9
14
6
67


Management Considerations:

Whole Profile
  • Plant Available Water Capacity (PAWC) is considered to be quite low as effective rooting depth is likely to be restricted to the surface horizons. The dense and coarsely structured upper subsoil is likely to restrict rooting depth.
Surface (A) Horizons
  • The surface soil has a low nutrient holding capacity. Organic matter is important for enhancing fertility of soils such as these with high sand contents.

  • The surface (A1) horizon disperses moderately after remoulding, indicating that structural degradation (e.g. surface sealing, exacerbated hardsetting, increased cloddiness) may occur if the soil is cultivated or overstocked in a moist to wet condition. Also, raindrop action on bare surface soil may also promote dispersion. Surface cover should be maintained to protect against raindrop damage.
Subsoil (B) Horizons
  • The coarsely structured upper subsoil is sodic and has a low exchangeable calcium to magnesium ratio (i.e. a high level of exchangeable magnesium relative to calcium). This may result in nutrient imbalances (e.g. calcium deficiency). At 50 cm the subsoil becomes strongly sodic and extremely sodic at 90 cm with strong dispersion. As a result of these conditions root and water movement is likely to be restricted in the subsoil. The use of gypsum in association with deep ripping, has been advocated by some researchers as an effective way to ameliorate sodic subsoils but this may not be an economic option. Deep ripping should not be carried out when the subsoil is in a moist to wet condition.

  • The subsoil displays vertic properties (i.e. slickensides) which indicates that significant shrinking and swelling occurs with wetting and drying cycles. This may disturb the roots of some plants. The shrinking and swelling also has engineering implications (e.g. disturbance to fence lines).
Comments from Landholder
  • Traffickable most times.
Profile Described By: Mark Imhof and Ian Sargeant (21/1/97).
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