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GP71

Location: Near Lake Wellington.Australian Soil Classification: Mottled-Sodic, Hypocalcic, Brown DERMOSOL.
Geology: Quaternary and Holocene swamp deposits.General Landscape Description: Low lying level plain.
Mapping Unit: Wandocka.Site Description: Grazing paddock.

Photo: Site G71 Landscape
Site GP71 Landscape

Soil Profile Morphology:

Surface Soil

A10-15 cmBlack (10YR2/1); clay loam; weak coarse blocky, parting to moderate medium polyhedral, parting to fine polyhedral structure; strong consistence dry; pH 5.8; gradual change to:

Photo: Site GP71 Profile
Site GP71 Profile
Subsoil

B2115-30 cmBlack (10YR2/1); light medium clay; moderate coarse prismatic structure; strong consistence dry; pH 6.4; gradual and wavy change to:

B2230-60 cmYellowish brown (10YR5/6) mixed with very dark greyish brown (10YR3/2); medium clay; strong coarse prismatic, parting to moderate coarse blocky structure; strong consistence dry; pH 8.2; gradual and wavy change to:

B2360-90 cmLight brown (7.5YR6/4) with brownish yellow (10YR6/8) mottles; medium clay; strong coarse prismatic, parting to moderate coarse blocky structure; strong consistence dry; pH 8.6; gradual and wavy change to:

B2490+ cmGrey (10YR6/1) with brownish yellow (10YR6/6) and light brown (7.5YR6/4) mottles; light medium clay; contains very few (1-2%) soft carbonate in patches; slightly micaceous; pH 8.9.

Key Profile Features:
  • Lack of strong texture contrast between surface (A) and subsoil (B21) horizons.

Soil Profile Characteristics:

Horizon
pH
Salinity Rating
Surface
(A1 horizon)
Moderately Acid
Low-Moderate
Non-Sodic
None1
Subsoil
(B21 horizon)
Slightly Acid
Very Low
Sodic
None2
Deeper Subsoil
(at 90 cm)
Strongly Alkaline
High
Extremely Sodic
Slight1
1 Slight dispersion after remoulding.
2 Complete dispersion after remoulding.


Graph: pH levels in Site G71





The soil profile becomes increasingly alkaline
with depth.
Graph: Sodicity levels in Site G71



The surface is non-sodic. The subsoil is
sodic becoming strongly sodic at 40 cm
depth.
Graph: Salinity levels in Site G71



The surface salinity is low to moderate. The
upper subsoil is very low becoming high at depth.
Graph: Clay% in Site G71




The clay content changes only gradually
with depth.

Horizon
Horizon Depth
(cm)
pH
(water)
pH
(CaCl2)
EC 1:5
NaCl
Exchangeable Cations
Ca
Mg
K
Na
meq/100g
A1
0-10
5.8
5
0.22
7
4.5
0.65
1.3
B21
10-30
6.4
5.2
0.1
5.9
5.8
0.34
1.2
B22
30-60
8.2
7.2
0.22
5.1
8.8
0.31
2.8
B23
60-90
8.6
7.7
0.47
3.8
6.6
0.23
4
B24
90+
8.9
8.3
1
3.5
5.7
<0.1
8.1



Horizon
Horizon Depth
(cm)
Exchangeable Aluminium
mg/kg
Exchangeable Acidity
meq/100g
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
16
13
16
5
35
22
28
B21
10-30
13.9
3
30
21
42
B22
30-60
16.2
3
38
22
33
B23
60-90
16
39
21
36
B34
90+
18.5

Management Considerations:

Whole Profile
  • Plant Available Water Capacity (PAWC) is considered to be low (estimated at 35 mm) for this soil profile. This is based on an estimated effective rooting depth of 15 cm (i.e. surface soil). The dense and coarsely structured subsoil is likely to restrict rooting depth. PAWC has been estimated using a model developed by Littleboy (1995) which uses analytical data for clay%, silt%, fine sand%, coarse sand % and wilting point.
Surface (A) Horizons
  • The surface (A1) horizon is non-sodic but disperses slightly after remoulding. This indicates that tillage or over-stocking of the soil whilst in a moist to wet condition may result in some structural degradation occurring (e.g. surface sealing, increased cloddiness). Raindrop action on bare soil may have a similar effect, so it is important to maintain surface cover.
Subsoil (B) Horizons
  • The dense and coarsely structured subsoil (B21) horizon is sodic and will restrict root and water movement.
  • The level of soluble salts becomes quite high in the deeper subsoil. This may restrict the growth of deeper rooted salt-sensitive species.
Profile Described By: Mark Imhof and Ian Sargeant (22/04/1998).
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