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Omeo (Symbol: Om)

EG206 | EG55 | Profile No. 215 | EG71

Geology
Palaeozoic granite and associated metamorphic gniesses.

Landform
Enclosed low hills and valleys. Apart from the slopes adjoining the drainage lines, typical slope gradients are 8-20% with a relief of 30-90 m. The map unit may be subdivided into three components: crest and long gentle slopes, low lying open depressions and steep slopes adjoining drainage lines.

Soils and landforms of the Omeo/Benambra and Tambo Valley region - soil-landform unit Omeo landform
Cleared low hills on granite north of Lake Omeo

Original vegetation
Montane grassy woodland.

Soils
Component 1: Soils on crests and long gentle slopes
The majority of the soils of this unit are texture contrast soils with strongly acidic to moderately acidic surface soils. The surface soils are mostly brown to dark brown weakly structured sandy loams and overlie a bleached subsurface of similar texture. The subsoils, which occur about 30 to 60 cm, are brown to yellowish brown medium clays, often with paler coloured mottling. Rock generally occurs deeper than 1 m. (Sites EG 55, EG 206, Profile No. 215 (Rowe, 1967)). Very occasionally quartz stones occur which tend to accumulate in the surface soil just above the subsoil clay. These are believed to be due to lag deposits from narrow quartz rich dykes which can form in the granite rock.

Soils and landforms of the Omeo/Benambra and Tambo Valley region - soil-landform unit Omeo soils1
Quartz stones in the surface soil down-slope from a quartz rich dyke (left hand side of photo).

Component 2: Soils in low lying open depressions
The surface soils are generally very dark grey sandy loams to sandy clay loams overlying dark grey coarsely structured medium to heavy clays. (Site EG116).

Component 3: Soils on steep slopes adjoining drainage lines
On the steep slopes rock outcrops are common. No soil pits were excavated on this component.

Soils and landforms of the Omeo/Benambra and Tambo Valley region - soil-landform unit Omeo soils2
Stone layer in cutting on Omeo – Swifts Creek road near
Livingston Road
Soils and landforms of the Omeo/Benambra and Tambo Valley region - soil-landform unit Omeo soils3
On steep slopes adjoining streams rock outcrops are common

Land use
All of the area is cleared and used for grazing.

Site EG206

Location: Omeo southGeo. Ref. 0557479E 5887924N
Australian soil classification: Eutrophic, Mottled-Subnatric, Brown SODOSOLSodic brown texture contrast soil
General landscape description: Undulating low hills
Geology: Palaeozoic granite
Site Description: Convex lower slope, 2 % slope to North
Land use: Grazing on annual pasture
Native vegetation: Montane grassy woodland
Mapping unit: Omeo (Component 1)

Soils and landforms of the Omeo/Benambra and Tambo Valley region - soil-landform unit Omeo EG206 landscape


Soil profile morphology

Surface soilSoils and landforms of the Omeo/Benambra and Tambo Valley region - soil-landform unit Omeo EG206 profile
A10 – 15 cmBrown (7.5YR4/2); sandy loam; weak medium (10 – 20 mm) polyhedral structure; firm consistence dry; clear change to:
A215 – 32 cmPale brown (10YR6/3) conspicuously bleached (10YR8/2d); sandy loam; apedal weak consistence dry; few (2 – 10 %) medium (2 – 6 mm) ferruginous concretions; sharp change to:
Subsoil
B2132 – 70 cmDark yellowish brown (10YR4/6) diffusely mottled with greyish brown (10YR5/2); medium clay; weak to moderate coarse (20 – 50 mm) prismatic structure; strong consistence dry; diffuse change to:
B2270 – 110+ cmBrown (10YR4/3); medium clay; moderate coarse (20 – 50 mm) lenticular structure; strong consistence dry
Key profile features
  • Strong texture contrast between the surface (A) horizon and the subsoil (B) horizon.
  • Conspicuously bleached subsurface (A2) horizon.
  • Vertic properties in the deep subsoil (i.e. slickensides).

Soil profile characteristics
pHSalinity ratingSodicityDispersionSlaking
Surface soil
(A1 horizon)
Strongly acidVery lowNon sodicSlightSlakes partially
Subsoil
(B21 horizon)
Slightly acidVery lowNon sodicNoneSlakes considerably
Deeper subsoil
(B22 horizon)
Slightly alkalineLowSodicNoneSlakes considerably

HorizonDepth

cm
Field texturepH
water
pH
CaCl
2
EC
dS/m
Coarse sand
%
Fine sand
%
Silt

%
Clay

%
Field cap.
% w/w
Wilt. point
% w/w
PAW*
water

% w/w
A10-15SL5.34.60.07223628723.35.218.1
A215-32SL5.44.7<0.05223728817.73.514.2
B2132-70MC6.55.70.141515125431.018.812.2
B2270-110MC7.36.60.31612 206038.822.216.6
* PAW is plant available water. This is the difference between the soil’s water content at field capacity and wilting point.

DepthOrg C#Total NFree
Fe2O3
% w/w
Exch.
Al
Exchangeable cations
meq/100 g
Ca:MgNa
%
cm%%ppmCaMgKNaTotalHCEC
0-152.10.15<102.70.560.160.123.55.69.14.81
15-320.59<0.05<101.40.36<0.050.111.92.14.03.83
32-700.556.37.40.261.3155.820.80.86
70-1100.38
# Organic carbon

Management considerations

Whole profile
  • The soil shows marked texture contrast between the surface soil and the subsoil.
  • Plant available water content is quite low based on a root depth of 45 cm. The dense and coarsely structured subsoil is likely to restrict root growth and confine most of the roots to the surface soil.
Surface (A) horizons
  • The low wilting points (5.2 and 3.5 %) of the surface soils indicates the plants are able to utilize very light rains when the soil is dry. However, due to the low water storage capacity, plants will soon suffer moisture stress unless further rains occur.
  • The surface soils are strongly acid. However the level of exchangeable aluminium is reasonably low 16 mg/kg) and is unlikely to affect the growth of aluminium sensitive species, except the most sensitive. Lime can be used to increase soil pH but a pH/aluminium test is best performed by taking samples across the paddock and bulked together. The use of test strips to observe lime response could be used as an aid in evaluating its cost/benefit. For this soil a response to lime (about 1-2 tonnes/ha) would be expected.
  • The organic matter content of the soil is moderate. Such levels result in a moderate structural condition and moderate structural stability. Careful pasture management is needed to maintain organic matter levels.
  • Potassium is too low for pastures and a response to potassium fertilisers would be anticipated.
  • Salinity is not a problem in the surface soil.
  • The nutrient holding capacity of the surface (A1 and A2) horizons is very low (based on the sum of the exchangeable calcium, magnesium, potassium and sodium cations).
  • The bleached subsurface layer lacks structure, sets hard when dry, impedes plant growth and slakes when wet.
Subsoil (B) horizons
  • The coarsely structured and high clay subsoil is sodic with a low calcium to magnesium ratio of 0.8. Water and root movement in the subsoil will be restricted by these conditions.
  • Root and water movement is likely to be restricted in the dense and coarsely structured subsoil. Mottled colours indicate the subsoil is imperfectly drained in wet periods.
  • This soil is highly prone to water erosion.
  • The roots tend to follow cracks between the soil aggregates and can only extract part of the soil water.
  • Salinity in the deep subsoil (70 cm) is higher than normal and may restrict the growth of deep rooted species.
Site EG55

Location: Upper Livingston RoadGeo. Ref. 0548363E 5884687N
Australian soil classification: Bleached, Eutrophic, Yellow CHROMOSOLYellow texture contrast soil
General landscape description: Rolling low hills
Geology: Ordovician metamorphosed sediments (gneiss)
Site Description: Lower slope (unspecified gradient)
Land use: Grazing on annual pasture
Native vegetation: Montane grassy woodland
Mapping unit: Omeo (Component 1)

Soils and landforms of the Omeo/Benambra and Tambo Valley region - soil-landform unit Omeo EG55 landscape


Soil profile morphology

Surface soilSoils and landforms of the Omeo/Benambra and Tambo Valley region - soil-landform unit Omeo EG55 profile
A10 – 10 cmDark brown (7.5YR3/2); sandy loam; weak polyhedral structure; clear change to:
A2110 – 25 cmYellowish brown (10YR5/4) conspicuously bleached dry; loamy sand; massive; gradual change to:
A2225 – 45 cmLight yellowish brown (2.5YR6/4) conspicuously bleached dry; coarse sandy loam; massive; common (10 – 20%) fine gravel (2 – 6 mm); clear change to:
Subsoil
B245 – 85 cmYellowish brown (10YR5/4); medium clay; strong coarse prismatic structure parting to angular blocky structure; slight (2 – 10%) fine gravel (2 – 6 mm), with increasing amounts of angular tabular pebbles (20 – 60 mm) becoming larger in size with depth; clear change to:
C85 cm+Decomposing rock

Soil profile characteristics
pHSalinity ratingSodicityDispersionSlaking
Surface soil
(A1 horizon)
Strongly acidVery lowNon sodicSlightWater stable
Subsurface
(A22 horizon)
Moderately acidVery lowNon sodicStrongSlakes partially
Deeper subsoil
(B2 Horizon)
Moderately acid Very lowNon sodicStrongSlakes partially

HorizonDepth

cm
Field texturepH
water
pH
CaCl
2
EC
dS/m
Coarse sand
%
Fine sand
%
Silt

%
Clay

%
Field cap.
% w/w
Wilt. point
% w/w
PAW*
water

% w/w
A10-10SL5.54.80.113335161120.57.513.0
A2110-25LS5.85.10.064036151014.63.611.0
A2225-45KSL5.850.053533131915.26.58.7
B245-85MC6.05.10.072019125030.717.313.4
* PAW is plant available water. This is the difference between the soil’s water content at field capacity and wilting point.

DepthOrg C#Total NFree
Fe2O3
% w/w
Exch.
Al
Exchangeable cations
meq/100 g
Ca:MgNa
%
cm%%ppmCaMgKNaTotalHCEC
0-104.00.2<102.91.60.710.115.49.114.51.91
10-25<101.00.690.390.062.23.45.61.51
25-45150.981.60.350.093.13.76.80.71
45-85152.05.00.870.258.27.715.90.42
# Organic carbon

Management considerations

Whole profile
  • The soil shows marked texture contrast between the surface soil and the subsoil.
  • Plant available water content is considered to be low, based on a root depth of 55 cm. The massive and hard setting nature of the subsurface soils (A21 and A22) and the dense and coarsely structured subsoil is likely to restrict root growth and confine most of the roots to the surface soil.
Surface (A) horizons
  • The low wilting points (7.5 and 3.6 %) of the surface soils indicates the plants are able to utilize very light rains when the soil is dry. However, due to the low water storage capacity, plants will soon suffer moisture stress unless further rains occur.
  • The surface soils are strongly acid. However the level of exchangeable aluminium is low (less than 10 mg/kg) and is unlikely to affect the growth of aluminium sensitive species, except the most sensitive. Here the subsurface soil is moderately acidic and a response to lime may not occur.
  • The organic matter content of the soil is high. Such levels result in a high structural condition and high structural stability. Careful pasture management is needed to maintain organic matter levels, particularly in these soils as they have a hard setting subsurface soil.
  • Potassium is high for pastures and no response to potassium fertilisers would be anticipated.
  • Salinity is not a problem in the surface soil.
  • The nutrient holding capacity of the surface (A1 and A2) horizons is low (based on the sum of the exchangeable calcium, magnesium, potassium and sodium cations).
  • The bleached subsurface layer lacks structure, sets hard when dry, impedes plant growth and slakes when wet.
Subsoil (B) horizons
  • The coarsely structured and high clay subsoil is non-sodic but has a low calcium to magnesium ratio of 0.4. Water and root movement in the subsoil will be restricted by these conditions. Little can be done to overcome these soil properties.
  • Root and water movement is likely to be restricted by the dense and coarsely structured subsoil.
  • This soil is highly prone to water erosion.
Profile No. 215 (Rowe, 1967)

Location: Bald Hills Road Omeo southNo Geo. Ref. available
Australian soil classification: Eutrophic, Subnatric, Yellow SODOSOLSodic yellow texture contrast soil
General landscape description: Undulating low hills
Geology: Palaeozoic granite
Site Description: None given
Land use: Grazing on annual pasture
Native vegetation: Montane grassy woodland
Mapping unit: Omeo (Component 1)

No photo available


Soil profile morphology

Not available, but observations of shallow road exposures along Bald Hills Road show surface soils overlying bleached subsurface soils with yellow brown clay subsoils.

Soil profile characteristics
HorizonDepth

cm
Field texturepH
water
pH
CaCl
2
EC
dS/m
Coarse sand
%
Fine sand
%
Silt

%
Clay

%
Field cap.
% w/w
Wilt. Point
% w/w
PAW*
water

% w/w
A10-8L5.60.0527262420
A215-30LS6.0<0.053936167
B2130-60C6.50.081615761
B2290-120C8.40.1641311217
* PAW is plant available water. This is the difference between the soil’s water content at field capacity and wilting point.

DepthOrg C#Total NFree
Fe2O3
% w/w
Exch.
Al
Exchangeable cations
meq/100 g
Ca:MgNa
%
cm%%ppmCaMgKNaTotalHCEC
0-81.70.151.04.61.70.40.16.87.414.22.71
15-300.20.020.81.30.60.10.052.12.95.02.21
30-602.93.712.40.31.918.320.528.80.37
90-1201.83.39.51.92.815.7-15.40.418
# Organic carbon

Management considerations

Surface (A) horizons
  • The soils are moderately acid but may show a slight response to lime applications.
  • The potassium levels are moderate and no response to potassium fertilisers would be expected.
  • Salinity is not a problem in the surface soil.
  • The nutrient holding capacity of the surface (A1 and A2) horizons is low to very low (based on the sum of the exchangeable calcium, magnesium, potassium and sodium cations).
Subsoil (B) horizons
  • The coarsely structured and high clay subsoil is sodic with very low calcium to magnesium ratio of 0.3. Water and root movement in the subsoil will be restricted by these conditions.
  • This soil is highly prone to water erosion.
Site EG71

Location: Omeo, Barbers LaneGeo. Ref. 0555912E 5892285N
Australian soil classification: Yellow SODOSOLSodic yellow texture contrast soil
General landscape description: Undulating low hills
Geology: Palaeozoic granite
Site Description: Hill-slope, gradient unspecified
Land use: Grazing on annual pasture
Native vegetation: Grassy woodland
Mapping unit: Omeo (Component 1)

Soil profile morphology

Surface soilSoils and landforms of the Omeo/Benambra and Tambo Valley region - soil-landform unit Omeo EG71 profile
A10 – 25/30 cmVery dark greyish brown (10YR3/2); sandy loam (light and high in organic matter); weak polyhedral structure; common (10 – 20%) fine (2 – 6 mm) gravel; clear wavy change to:
A225/30 – 50/55 cmVery pale brown (10YR7/3) conspicuously bleached (10YR8/2d); loamy sand; massive; strong consistence dry; slight (2 – 10%) fine (2 – 6 mm) gravel; clear wavy change to:
Subsoil
B2150/55 – 100 cmYellowish brown (10YR5/4); medium heavy clay; coarse prismatic structure parting to angular blocky structure; strong consistence dry; slight (2 – 10%) fine (2 – 6 mm) gravel.
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