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GP36

Location: Heyfield.Australian Soil Classification: Sodic, Eutrophic, Red DERMOSOL.
Geology: Quaternary alluvial prior stream deposits.General Landscape Description: Level plain with prior stream activity.
Mapping Unit: Tinamba.Site Description: Dairy grazing paddock.

Photo: Site G36 Landscape
Site GP36 Landscape


Soil Profile Morphology:

Surface Soil

A10-5 cmDark yellowish brown (10YR4/4); silty clay loam; moderate medium polyhedral, parting to weak fine polyhedral structure; strong consistence dry; pH 6.5; clear change to:

Photo: Site G36 Profile
Site GP36 Profile
A25-20 cmBrown (10YR5/3) sporadically bleached (10YR7/3d) with strong brown (7.5YR5/6) mottles; silty clay loam; structureless; very strong consistence dry; pH 6.9; clear and wavy change to:

Subsoil

B120-30 cmYellowish red (5YR5/8); silty clay loam; weakly structured; strong to very strong consistence dry; pH 7.6; gradual change to:

B2130-50 cmYellowish red (5YR5/8) silty clay; weakly structured; firm consistence moist; pH 7.7; clear change to:

B2250-90 cmRed (2.5YR5/8); organic stains on ped faces; medium clay; moderate coarse prismatic, parting to strong coarse blocky, parting to moderate blocky structure; shiny faced peds [organic staining on ped faces]; strong consistence dry; pH 7.8; gradual change to:

B2390+ cmRed (2.5YR5/8); light medium clay; strong coarse prismatic, parting to strong coarse to medium polyhedral structure; shiny faced peds; contains a few (10%) manganese flecks and some fine mica, as well as pockets of reddish yellow (5YR6/6) fine sand; pH 8.0.

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

Soil Profile Characteristics:

Horizon
pH
Salinity Rating
Surface
(A1 horizon)
Slightly Acid
Low
Sodic
None1
Subsoil
(B21 horizon)
Slightly Alkaline
Very Low
Strongly Sodic
Slight2
Deeper subsoil
(at 1 m)
Moderately Alkaline
Low
Strongly Sodic
Strong
1 Moderate dispersion remoulded.
2
Complete dispersion after remoulding.

Graph: pH levels in Site G36





The surface soil is slightly acid. The
subsoil is slightly alkaline, becoming
moderately alkaline at 1 m.
Graph: Sodicity levels in Site G36



The surface soil is sodic. The subsoil is
strongly sodic.
Graph: Salinity levels in Site G36



The level of soluble salts is low throughout
the soil profile.
Graph: Clay% in Site G36



The clay content gradually increases with
depth.

Horizon
Horizon Depth
(cm)
pH
(water)
pH
(CaCl2)
EC 1:5
Exchangeable Cations
Ca
Mg
K
Na
meq/100g
A1
0-5
6.5
5.7
0.13
7.9
3.3
0.22
1.2
A2
5-20
6.9
5.8
0.08
4.8
1.8
0.2
0.87
B1
20-30
7.6
6.3
0.07
2.7
0.8
0.4
0.9
B21
30-50
7.7
6.3
0.07
2.1
0.9
0.1
1.2
B22
50-90
7.8
6.3
0.08
2.7
4.2
0.2
2.3
B23
90+
8
6.7
0.11
2.6
4.7
0.2
2.2

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
7
21
39
27
A2
5-20
11
1
26
44
28
B1
20-30
9
1
26
43
29
B21
30-50
11
1
24
43
32
B22
50-90
17
1
14
29
55
B23
90+
18
0
13
35
51


Management Considerations:

Surface (A) Horizons
  • The surface (A1) horizon is sodic but does not disperse unless remoulded. Moderate dispersion occurs after remoulding, which indicates that structural degradation (e.g. 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 (i.e. 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 rain falls occur.

  • The presence of sporadic bleaching in the subsurface (A2) horizon indicates that some periodic waterlogging occurs above the more slowly permeable subsoil.
Subsoil (B) Horizons
  • The soil texture of the subsoil increases gradually from the boundary of the surface horizon. This will present less of a physical barrier to water movement as compared to Sodosols in the region where there is a strong texture contrast between surface and subsoil horizons. However, the subsoil is strongly sodic and disperses (strongly at depth) which will result in conditions restricting water movement. Deep ripping (with gypsum application) has been recommended by some researchers as an effective ameliorative technique for sodic subsoils. This may not be an economically viable option.
Profile Described By: Mark Imhof and Ian Sargeant (21/1/97).
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