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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.


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.


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.

Stone layer in cutting on Omeo – Swifts Creek road near Livingston Road

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 south	Geo. Ref. 0557479E 5887924N
Australian soil classification: Eutrophic, Mottled-Subnatric, Brown SODOSOL	Sodic 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)

Soil profile morphology

Surface soil
A1	0 – 15 cm	Brown (7.5YR4/2); sandy loam; weak medium (10 – 20 mm) polyhedral structure; firm consistence dry; clear change to:
A2	15 – 32 cm	Pale 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
B21	32 – 70 cm	Dark 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:
B22	70 – 110+ cm	Brown (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

	pH	Salinity rating	Sodicity	Dispersion	Slaking
Surface soil (A1 horizon)	Strongly acid	Very low	Non sodic	Slight	Slakes partially
Subsoil (B21 horizon)	Slightly acid	Very low	Non sodic	None	Slakes considerably
Deeper subsoil (B22 horizon)	Slightly alkaline	Low	Sodic	None	Slakes considerably

Horizon	Depth cm	Field texture	pH water	pH CaCl2	EC dS/m	Coarse sand %	Fine sand %	Silt %	Clay %	Field cap. % w/w	Wilt. point % w/w	PAW* water % w/w
A1	0-15	SL	5.3	4.6	0.07	22	36	28	7	23.3	5.2	18.1
A2	15-32	SL	5.4	4.7	<0.05	22	37	28	8	17.7	3.5	14.2
B21	32-70	MC	6.5	5.7	0.14	15	15	12	54	31.0	18.8	12.2
B22	70-110	MC	7.3	6.6	0.31	6	12	20	60	38.8	22.2	16.6

* PAW is plant available water. This is the difference between the soil’s water content at field capacity and wilting point.

Depth	Org C#	Total N	Free Fe2O3 % w/w	Exch. Al	Exchangeable cations meq/100 g							Ca:Mg	Na %
cm	%	%		ppm	Ca	Mg	K	Na	Total	H	CEC
0-15	2.1	0.15		<10	2.7	0.56	0.16	0.12	3.5	5.6	9.1	4.8	1
15-32	0.59	<0.05		<10	1.4	0.36	<0.05	0.11	1.9	2.1	4.0	3.8	3
32-70	0.55				6.3	7.4	0.26	1.3	15	5.8	20.8	0.8	6
70-110	0.38

# 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 Road	Geo. Ref. 0548363E 5884687N
Australian soil classification: Bleached, Eutrophic, Yellow CHROMOSOL	Yellow 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)

Soil profile morphology

Surface soil
A1	0 – 10 cm	Dark brown (7.5YR3/2); sandy loam; weak polyhedral structure; clear change to:
A21	10 – 25 cm	Yellowish brown (10YR5/4) conspicuously bleached dry; loamy sand; massive; gradual change to:
A22	25 – 45 cm	Light yellowish brown (2.5YR6/4) conspicuously bleached dry; coarse sandy loam; massive; common (10 – 20%) fine gravel (2 – 6 mm); clear change to:
Subsoil
B2	45 – 85 cm	Yellowish 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:
C	85 cm+	Decomposing rock

Soil profile characteristics

	pH	Salinity rating	Sodicity	Dispersion	Slaking
Surface soil (A1 horizon)	Strongly acid	Very low	Non sodic	Slight	Water stable
Subsurface (A22 horizon)	Moderately acid	Very low	Non sodic	Strong	Slakes partially
Deeper subsoil (B2 Horizon)	Moderately acid	Very low	Non sodic	Strong	Slakes partially

Horizon	Depth cm	Field texture	pH water	pH CaCl2	EC dS/m	Coarse sand %	Fine sand %	Silt %	Clay %	Field cap. % w/w	Wilt. point % w/w	PAW* water % w/w
A1	0-10	SL	5.5	4.8	0.11	33	35	16	11	20.5	7.5	13.0
A21	10-25	LS	5.8	5.1	0.06	40	36	15	10	14.6	3.6	11.0
A22	25-45	KSL	5.8	5	0.05	35	33	13	19	15.2	6.5	8.7
B2	45-85	MC	6.0	5.1	0.07	20	19	12	50	30.7	17.3	13.4

* PAW is plant available water. This is the difference between the soil’s water content at field capacity and wilting point.

Depth	Org C#	Total N	Free Fe2O3 % w/w	Exch. Al	Exchangeable cations meq/100 g							Ca:Mg	Na %
cm	%	%		ppm	Ca	Mg	K	Na	Total	H	CEC
0-10	4.0	0.2		<10	2.9	1.6	0.71	0.11	5.4	9.1	14.5	1.9	1
10-25				<10	1.0	0.69	0.39	0.06	2.2	3.4	5.6	1.5	1
25-45				15	0.98	1.6	0.35	0.09	3.1	3.7	6.8	0.7	1
45-85				15	2.0	5.0	0.87	0.25	8.2	7.7	15.9	0.4	2

# 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 south	No Geo. Ref. available
Australian soil classification: Eutrophic, Subnatric, Yellow SODOSOL	Sodic 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

Horizon	Depth cm	Field texture	pH water	pH CaCl2	EC dS/m	Coarse sand %	Fine sand %	Silt %	Clay %	Field cap. % w/w	Wilt. Point % w/w	PAW* water % w/w
A1	0-8	L	5.6		0.05	27	26	24	20
A2	15-30	LS	6.0		<0.05	39	36	16	7
B21	30-60	C	6.5		0.08	16	15	7	61
B22	90-120	C	8.4		0.16	41	31	12	17

* PAW is plant available water. This is the difference between the soil’s water content at field capacity and wilting point.

Depth	Org C#	Total N	Free Fe2O3 % w/w	Exch. Al	Exchangeable cations meq/100 g							Ca:Mg	Na %
cm	%	%		ppm	Ca	Mg	K	Na	Total	H	CEC
0-8	1.7	0.15	1.0		4.6	1.7	0.4	0.1	6.8	7.4	14.2	2.7	1
15-30	0.2	0.02	0.8		1.3	0.6	0.1	0.05	2.1	2.9	5.0	2.2	1
30-60			2.9		3.7	12.4	0.3	1.9	18.3	20.5	28.8	0.3	7
90-120			1.8		3.3	9.5	1.9	2.8	15.7	-	15.4	0.4	18

# 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 Lane	Geo. Ref. 0555912E 5892285N
Australian soil classification: Yellow SODOSOL	Sodic 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 soil
A1	0 – 25/30 cm	Very 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:
A2	25/30 – 50/55 cm	Very 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
B21	50/55 – 100 cm	Yellowish 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.