Tarravale (Symbol: Tv)

EG25 | EG217

Geology
Devonian marine sediments, predominantly limestone. This map unit is mostly confined to the geological map unit known as the Taravale Formation, described as marlstone. The other two limestone formations, known as the Buchan Formation and the Murrindal Formation, have been combined in this report and called the Buchan map unit. The underlying rocks are classified as recrystallised limestone and are much harder than the marlstone.

Landform
Rolling low hills to steep hills with an elevation range of about 80 to 350 m. The relief is less than 300 m with much of the land having lower relief of less than 90 m. Most of the area comprises long moderately inclined slopes with small areas of alluvial fans and drainage lines.


Rolling and steep hills on limestone north of Buchan

Native vegetation Grassy woodland. Soils Component 1: Soils on long moderately inclined slopes. The soils of this map unit are quite variable in terms of colour, depth, and presence of stone above the marlstone. There may be some relationship between slope and aspect, but this could not be determined during this study. Other than the photographs of the pits, the following photographs show some of this variability. Most soils are alkaline and since lime occurs within the root zone, are unlikely to show any response to additional lime. Component 2: Soils on alluvial fans and drainage lines. No soils were examined.

Left photo: Shallow dark brown soil Right photo: Deep red-brown soil on marlstone

Site EG25

Location: Buchan Township	Geo. Ref. 603500E 5849100N
Australian soil classification: Haplic, Calcic, Brown DERMOSOL	Brown gradational soil on limestone
General landscape description: Steep hills
Geology: Devonian limestone
Site description: Mid slope, NE aspect, 27% slope
Land use: Road reserve
Native vegetation: Grassy woodland
Map unit: Taravale (Component 1)

Soil profile morphology

Surface soil
A	0 – 25 cm	Very dark brown (7.5YR4/2); clay loam (sub plastic); strong medium polyhedral structure; moderate amount (20-50%) subangular limestone pebbles (6 – 20 mm); clear change to:
Subsoil
B	25 – 65 cm	Dark brown (7.5YR4/3); heavy clay; strong medium prismatic parting to fine prismatic structure; common (10-20%) subangular limestone pebbles (6 – 20 mm; abrupt change to:
C	65– 85+ cm	Light yellowish brown (10YR6/4) rubbly limestone.
Key profile features High clay content throughout. Strongly structured and deep soil. *As the roadside cutting did not have a vertical slope the measurements on the tape will not show the true vertical depth.

Soil profile characteristics

	pH	Salinity rating	Sodicity	Dispersion	Slaking
Surface soil (A horizon)	Moderately acid	Very low	Non sodic	None	Water stable
Subsoil (B horizon)	Slightly acid	Very low	Non sodic	None	Water stable

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
A	0-25	CL(+)	5.9	5.3	0.1	12	19	26	40	33.8	16.6	17.2
B	25-65	HC	6.7	5.9	0.1	2	6	11	78	40.9	25.3	15.6

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

Depth	OrgC#	Total N	Free Fe2O3	Exch. Al	Exchangeable cations cmol(+)/kg							Ca:Mg	ESP
cm	%	%	% w/w	ppm	Ca	Mg	K	Na	Total	H	CEC
0-25	2.3	0.18			11	1.4	0.72	0.17	13.3	9.1	22.4	7.9	1
25-65					19	2.2	0.71	0.27	22.2	9.4	31.6	8.7	1

# Organic carbon

Management considerations

Whole profile

• Plant available water (PAW) here is considered to be high, estimated to be 115 mm. Because of the variability in the depth of soil cover within this map unit, many soils will have low to very low water-holding capacity. Effective rooting depth is limited by the depth to rock.

Surface (A) horizons

• The surface soil here is moderately acid. However because the soil has limestone in the subsoil, no response to additional lime would be anticipated.
• The soil is low in soluble salts.
• Potassium levels are high and plant responses to potassium fertiliser are unlikely.
• The nutrient holding capacity of the surface A horizon is high (based on the sum of the exchangeable calcium, magnesium, potassium and sodium cations).

Subsoil (B) horizons

• The subsoil would be relatively well drained and strongly structured which will enable plant roots to penetrate easily until they reach rock.

Site EG217

Location: Buchan	Geo. Ref. 0602900E 5847500N
Australian soil classification: Melanic, Calcic, Red DERMOSOL	Red gradational soil on limestone
General landscape description: Rolling hills
Geology: Devonian limestone, Taravale Formation
Site description: Upper slope, 5% slope, western aspect
Land use: Grazing
Native vegetation: Grassy woodland
Map unit: Buchan (Component 1)

Soil profile morphology

Surface soil
A1	0 – 20 cm	Dark reddish brown (5YR3/2); heavy clay loam (subplastic); strong fine (2 – 5 mm) granular structure; few (2 – 10%) subrounded limestone pebbles (6 – 20 mm); weak consistence moist; clear change to:
Subsoil
B21	20 – 40/50 cm	Dark reddish brown (5YR3/4); medium clay; strong fine (5 – 10 mm) polyhedral structure; common (10 – 20%) subangular limestone pebbles (20 – 60 mm); very firm consistence moist; clear and wavy change to:
B22	40/50 -60 mm	Light brown (7.5YR6/4) mottled with strong brown (7.5YR5/6); silty clay; weak medium (10 – 20 mm) polyhedral structure; few (2 – 10%) subangular limestone pebbles (20 – 60 mm); firm consistence dry; clear change to:
C	60 – 100 mm	White (7.5YR8/1), soft limestone; few (2 – 10%) subangular limestone pebbles (20 – 60 mm); limestone becoming stronger with depth

Key profile features

• Lack of texture contrast between the surface (A) horizon and the subsoil (B) horizon.
• Moderately shallow profile depth to limestone.

Soil Profile Characteristics

	pH	Salinity rating	Sodicity	Dispersion	Slaking
Surface soil (A1 horizon)	Slightly alkaline	Very low	Non sodic	None	Slake considerably
Subsoil (B21 horizon)	Moderately alkaline	Very low	Non sodic	None	Slakes partially
Deeper subsoil (60-100 cm)	Strongly alkaline	Very low	Non sodic	None	Slakes considerably

Horizon	Depth cm	Field texture	pH water	pH CaCl2	EC dS/m	Coarse sand %	Fine sand %	Silt %	Clay %	Loss on acid treat-ment1	Field cap. % w/w	Wilt. point % w/w
A1	0-20	CL	7.7	7.2	0.08	3	9	23	49	6	38.5	22.8
B21	20-40/45	MC	8.2	7.6	0.06	8	9	14	37	28	33.4	18.8
B22	40-60	ZC	8.6	7.8	0.04	12	16	9	26	37	34.2	14.7
C	60-100	Lime-stone	8.8	7.8	0.03	19	9	8	16	38	36.3	10.4

¹The loss on acid treatment is due to the presence of lime (calcium carbonate) in the soil.

Depth	OrgC#	Total N	Free Fe2O3	Exch. Al	Exchangeable cations cmol(+)/kg							Ca:Mg	ESP
cm	%	%	% w/w	ppm	Ca	Mg	K	Na	Total	H	CEC
0-20	4.3	0.36		<10	38	0.99	0.52	0.17	39.7		39.7	38	<1
20-40/45	2.2	0.17		<10	34	0.6	0.38	0.13	35.1		35.1	57	<1
40-60	0.51	<0.05		<10	25	0.22	<0.05	0.13	25.3		25.3	120	<1
60-100	0.31	<0.05		<10	24	0.28	<0.05	0.11	24.4		24.4	88	<1

# Organic carbon

Management considerations

Whole profile

• Plant available water (PAW) here is considered to be moderate, estimated to be 90 mm. Because of the variability in the depth of soil cover within this map unit, many soils will have low to very low water-holding capacity. Effective rooting depth is limited to the depth to rock.

Surface (A) horizons

• The surface soil here is slightly alkaline and no response to additional lime would occur.
• The soils are low in soluble salts.
• Potassium levels are moderate and plant responses to potassium fertiliser are unlikely given the present grazing management.
• The nutrient holding capacities of the surface (A1 and B21) horizons are high (based on the sum of the exchangeable calcium, magnesium, potassium and sodium cations).

Subsoil (B) horizons

• The subsoil is well drained as there is no sharp increase in clay content at the A/B boundary.
• The subsoil horizons are non-sodic and strongly structured, which will enable plant roots to penetrate easily until they reach decomposing limestone that acts as both a physical and chemical barrier.