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GP68

Location: Bundalaguah.Australian Soil Classification: Melanic, (& Sodic) Hypocalcic, Brown CHROMOSOL.
Geology: Quaternary prior stream deposits.General Landscape Description: Level plain above present flood plain (adjacent to prior stream levee bank).
Mapping Unit: Tinamba [This soil is equivalent to Acre clay loam as described by Skene and Walbran (1948)].Site Description: Dairy grazing paddock.

Photo: Site G68 Landscape
Site GP68 Landscape

Soil Profile Morphology:

Surface Soil

A10-10 cm Very dark greyish brown (10YR3/2); fine sandy clay loam; moderate medium polyhedral, parting to fine polyhedral structure; very firm consistence dry; pH 5.8:

Photo: Site G68 Profile
Site GP68 Profile
A2110-30 cmVery dark greyish brown (10YR3/2); conspicuously bleached (10YR6/2d); fine sandy clay loam; moderate medium polyhedral, parting to moderate fine polyhedral structure; rusty root channel mottling present; strong consistence dry; pH 6.4:

A2230-45 cmBrown (10YR5/3); sporadically bleached; fine sandy clay loam; weak structure; strong consistence dry; pH 7.7:

Subsoil

B2145-80 cmStrong brown (7.5YR5/6); medium clay; strong coarse prismatic, parting to strong coarse blocky structure; strong consistence dry; very many (50-60%) dark stains on ped faces; pH 8.1:

B2280-100 cmLight reddish brown (5YR6/4); light medium clay; strong consistence dry; contains very few (1%) carbonate/silica nodules (5-10 mm in size); pH 9.0:

B23100+ cmLight brownish grey (10YR6/2) with (40%) brownish yellow (10YR6/6) mottles; light medium clay; strong coarse prismatic, parting to moderate coarse blocky structure; strong consistence dry; pH 9.1.
Key Profile Features:
  • Strong texture contrast between surface (A) horizons and subsoil (B21) horizon.
  • Conspicuously bleached subsurface (A2) horizon.
Soil Profile Characteristics:

Horizon
pH
Salinity Rating
Surface
(A1 horizon)
Moderately Acid
Moderate
Non-Sodic
None
Subsoil
(B21 horizon)
Moderately Alkaline
Low
Non-Sodic
Slight1
Deeper Subsoil
(at 1 m)
Strongly Alkaline
Moderate
Strongly Sodic
Slight1
1 Complete dispersion after remoulding.

Graph: pH levels in Site G68





The soil profile becomes increasingly
alkaline with depth.
Graph: Sodicity levels in Site G68


The surface and upper subsoil is
non-sodic. The deeper subsoil
becomes sodic at 65 cm and strongly
sodic at 85 cm depth.
Graph: Salinity levels in Site G68



The surface salinity rating is moderate.
The subsoil rating is low becoming
moderate with depth.
Graph: Clay% in Site G68



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
0-10
5.8
5.3
0.47
<0.03
13
4.2
2
0.1
A21
10-30
6.4
5.6
0.11
6.1
3
1.4
0.24
A22
30-45
7.7
6.8
0.09
4.3
3.7
1.2
0.35
B21
45-80
8.1
7.4
0.25
<0.03
4.7
7.5
1.8
0.5
B22
80-100
9
8.4
0.54
0.06
2.5
8
0.9
2.3
B23
100+
9.1
8.3
0.6
0.11



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
<10
17.3
9
24
27
26
A21
10-30
11.5
5
27
37
27
A22
30-45
10.4
3
28
39
29
B21
45-80
16.4
2
20
28
49
B22
80-100
16.6
1
11
44
4
1.4B23
100+

Management Considerations:

Whole Profile
  • Plant Available Water Capacity (PAWC) is considered to be moderate (estimated at 95 mm) for this soil profile. This is based on an estimated effective rooting depth of 45 cm (i.e. surface soil). The denser and more coarsely structured deeper subsoil is likely to restrict rooting depth, although not to the same extent as some of the more sodic subsoils in the region. 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 level of soluble salts in the surface is moderate and may restrict the growth of salt sensitive species. These levels may be unnaturally high due to the effects of the dry season at the time of sampling (i.e. summer 1997) and are likely to decline following heavy rainfall and/or irrigation.
  • The surface (A1) horizon has a high nutrient holding capacity (based on the sum of the exchangeable calcium, magnesium and potassium cations). The high levels of organic matter at this site are important for enhancing soil fertility as well as water holding capacity and surface soil structure. Nitrogen levels are high reflecting the high organic matter levels at this site.
  • The presence of bleaching and rusty root channel mottling in the subsurface (A2) horizon indicates that periodic waterlogging occurs above the more slowly permeable subsoil.
Subsoil (B) Horizons
  • The dense and coarsely structured upper subsoil is non-sodic but disperses slightly. Root and water movement will be restricted in the subsoil although not as significantly as Sodosols in the region.
Profile Described By: Mark Imhof and Ian Sargeant (22/04/1998).
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