Victorian Resources Online (archived)

EGC208

Location: Dargo

Australian Soil Classification: Bleached, Eutrophic, Brown CHROMOSOL

Map Unit: Dargo (Component 1)
Previous Site Name: EG208

General Landscape Description: Rolling low hills
Site description: Simple mid slope - 8% facing north
Land Use: Grazing
Native Vegetation: Grassy woodland
Geology: Silurian granite (metamorphosed Ordovician sediments upslope)

Rolling low hills of the Dargo map unit. The steep to very steep hills on the right are comprised of metamorphosed
Ordovician sediments and mapped as the Talbotville map unit. The excavator is back- filling the soil pit.

Soil Profile Morphology:

Surface Soil

A1	0 – 10 cm	Dark brown (7.5YR3/2); sandy loam; moderate fine (2 – 5 mm) granular structure; weak consistence, moist; few (2 - 10 %) coarse angular pebbles (20 – 60 mm) derived from metamorphosed sediments upslope; pH 5.1; clear change to:	EG208 profile
A2	10 – 35 cm	Brown (7.5YR5/4), conspicuously bleached (7.5YR7/1d); sandy loam; apedal; weak consistence dry; abundant (50 – 90%) angular cobbles (60 -200 mm) derived from metamorphosed sediments upslope; pH 6.0; sharp change to:
Subsoil
B21	36 – 70 cm	Dark red (2.5YR3/6); medium heavy clay; strong coarse polyhedral structure; strong consistence dry; pH 7.4; gradual change to:
B22	70 – 120 cm	Dark yellowish brown (10YR5/4) mottled with yellowish red; medium clay; strong coarse polyhedral structure; strong consistence dry; pH 8.2; diffuse change to:
B23	120 – 180 cm	Dark yellowish brown (10YR5/4) mottled with yellowish red; medium clay, slightly sandy; moderate coarse lenticular structure; strong consistence dry.

Key Profile Features:

Sharp texture contrast between the surface soil (A horizons) and the subsoil (B horizons)
Stone layer just above the clay subsoil.

Soil Profile Characteristics:

-	pH	Sodicity	Dispersion
Surface soil (A horizon)	Strongly acid	Non-sodic	Nil
Subsurface soil (A2 horizon)	Moderately acid	Non-sodic	Slight
Subsoil (B21 horizon)	Slightly alkaline	Non-sodic	Nil

Chemical and Physical Analysis:

Horizon	Horizon Depth (cm)	pH (water)	pH (CaCl₂)	EC dS/m	Organic Carbon %	Exchangeable Aluminium ppm	Exchangeable Acididty meq/100g	Exchangeable Cations				Coarse Sand (0.2-2.0 mm) %	Fine Sand (0.02-0.2 mm) %	Silt (0.002-0.02 mm) %	Clay (<0.002 mm) %	Field Capacity % w/w	Wilting Point % w/w
								Ca	Mg	K	Na
								meq/100g
A1	0-10	5.1	4.4	0.06	4.4	25	11	2.8	0.82	0.3	0.07	20	53	11	10	21.9	8.6
A2	10-35	6.0	5.1	<0.05	1.0	<10	2.6	2.6	0.63	0.12	0.06	18	58	14	8	18.0	3.4
B21	35-70	7.4	6.4	0.07	0.56			9	13	0.3	0.74	5	21	12	59	40.6	23.6
B22	70-120	8.2	7.2	0.08	<0.30			9.6	15	0.25	1.2	11	34	16	35	34.1	17.6

Management considerations

Whole profile

Plant available water content for this profile is considered to be very low, estimated at 25 mm, as the effective rooting depth, considered here to be 40 cm, is largely limited by the dense and coarsely structured nature of the subsoil.

Surface (A) horizons

The low wilting points (8.6 and 3.4 %) 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 soil is strongly acid. However the level of exchangeable aluminium is reasonably low (25 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 preformed by taking samples across the paddock and bulked together. The use of test strips to observe lime response should 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 surface soil is high. Such levels result in a good surface structure and stability.
Potassium is at a low level for pastures and a response to potassium fertilisers would be expected.
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).

Subsoil (B) horizons

Root and water movement is likely to be restricted in the dense and coarsely structured subsoil although the red colour of the subsoil indicates the soil is generally well drained.
The roots tend to follow cracks between the soil aggregates and can only extract part of the soil water.
The subsoil and the deep subsoil are slightly dispersive but slake considerably. If the subsoil is exposed, for example by a gully head, headward erosion is highly likely.

Profile Described By: Ian Sargeant, Heather Adams and Julieanne Sargant, June 2009.

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