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GP34

Location: Toongabbie.Australian Soil Classification: Eutrophic, Mottled-Hypernatric, Brown SODOSOL.
Great Soil Group: Solodic.Geology: Pleistocene alluvial deposits.
General Landscape Description: Level plain. Mapping Unit: Stratford.
Site Description: Road reserve.Native Vegetation: The original vegetation included yellow box and red stringybark.

Photo: SIte G34 Landscape
Site GP34 Landscape


Soil Profile Morphology:

Surface Soil

A1 0-5 cmDark brown (10YR3/3); fine sandy loam; weak medium blocky structure; weak to firm consistence dry; pH 5.7:

Graph: Site G34 Profile
Site GP34 Profile
A2 5-20 cmPale brown (7.5YR7/4) conspicuously bleached (10YR8/2d); fine sandy loam; pH 5.7; abrupt change to:

Subsoil

B2120-70cmYellowish brown (10YR5/4) with slight brownish yellow (10YR6/8) mottles [at depth the colour becomes yellowish brown (10YR5/6) with some red (2.5YR5/8) mottles]; medium heavy clay; strong coarse blocky, parting to moderate medium blocky structure; very strong consistence dry; pH 7.8:

B2270-100 cmBrownish yellow (10YR6/6) with light brownish yellow (10YR6/8) mottles; light clay; strong coarse blocky structure; pH 8.5.

Key Profile Features:
  • Strong texture contrast between surface (A) horizon (13% clay) and strongly sodic subsoil (B21) horizon (44% clay).
  • Conspicuously bleached subsurface (A2) horizon.
Soil Profile Characteristics:

Horizon
pH
Salinity Rating
Surface
(A1 horizon)
Moderately Acid
Low
Non-Sodic
None1
Subsoil
(B21 horizon)
Slightly Alkaline
Low
Strongly sodic
Complete
Deeper subsoil
(at 90 cm)
Moderately Alkaline
Medium
Strongly sodic
Complete
1 Moderate dispersion after remoulding.


Graph: pH levels in Site G34





The surface is moderately acid. The
subsoil is slightly alkaline; becoming
moderately alkaline at 60 cm.
Graph: Sodicity levels in Site G34



The subsoil is strongly sodic throughout.
Graph: Salinity in Site G34



The salinity rating is low; becoming
moderate at 1 metre depth.
Graph: Clay% in Site G34



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
0-5
5.7
4.7
0.07
2.5
2.2
0.3
0.34
A2
5-20
5.7
4.6
0.11
1.2
2.8
0.29
0.83
B21
20-70
7.8
6.8
0.31
0.07
1.9
7
0.3
3.1
B22
70-100
8.5
7.4
0.4
0.08
1.7
7.1
0.2
4
B23
100+
7.5
7.2
2.6
0.66
0.6
7.6
0.2
5.7

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
0-5
7
9
51
24
13
A2
5-20
7
5
50
25
19
B21
20-70
16
3
33
18
44
B22
70-100
17
3
33
18
46
B23
100+
4
25
25
46


Management Considerations:

Whole Profile
  • Plant Available Water Capacity (PAWC) is considered to be low for this profile as effective rooting depth will be limited to the surface horizons due to the dense and coarsely structured nature of the strongly sodic subsoil.
Surface (A) Horizons
  • The surface (A1) horizon has a very high fine sand and silt content. Soils such as these rely to a large extent on organic matter for maintaining aggregation.

  • The nutrient holding capacity of the surface horizons is low (based on the sum of the exchangeable basic cations). Organic matter is also important for nutrient storage on such soils.

  • The surface (A1) horizon is non-sodic. Moderate dispersion occurs after remoulding, indicating that structural degradation (eg. surface sealing, 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.

  • The low wilting point value (7%) of the surface (A1) horizon indicates that plants will be able to utilise very light rains when the soil is dry. However, due to the low water storage capacity, plants will soon suffer moisture stress unless further rainfall occurs.

  • Infiltration will be high in the surface (A1) horizon due to the high sand content. However, in the subsurface (A2) horizon the presence of conspicuous bleaching indicates that periodic waterlogging occurs above the more slowly permeable subsoil. This bleached horizon is likely to become ‘spewy’ when saturated.
Subsoil (B) Horizons
  • The coarsely structured upper subsoil is strongly sodic (with a low exchangeable calcium to magnesium ratio of 0.3) and complete dispersion occurs in water. Root and water movement will be significantly restricted in the subsoil due to these conditions. Deep ripping with gypsum application, has been advocated by some researchers as an effective ameliorating technique for sodic subsoils. However, this may not be an economical alternative. Deep ripping should not be carried out if the subsoil is in a moist-wet condition.

  • The subsoil is mottled throughout which indicates imperfect subsoil drainage.

  • The subsoil becomes moderately saline at about 1 metre depth which may restrict the growth of deeper-rooted salt sensitive plant species.
Profile Described By: Mark Imhof and Ian Sargeant (20/1/97).
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