EGC204

Location: Benambra (East of township)

Australian Soil Classification: Sodic, Eutrophic, Black CHROMOSOL

Map Unit: Benambra (Component 1)
Previous Site Name: EG204

General Landscape Description: Almost level plain
Land Use: Grazing on annual pasture
Native Vegetation: Montane grassland
Geology: Pleistocene to recent alluvial deposits

Soils and landforms of the Omeo/Benambra and Tambo Valley region - soil-landform unit Benambra EG204 landscape

Soil Profile Morphology:

Surface soil
A1	0 – 15 cm	Very dark greyish brown (10YR3/2); clay loam; moderate coarse (20 – 50 mm) polyhedral structure; firm consistence dry; abrupt change to:
Subsoil
B21	15 – 45 cm	Very dark grey (10YR3/1); medium clay; strong very coarse (> 50 mm) prismatic structure; very firm to strong consistence dry;
B22	45 – 80 cm	Brown (10YR5/3); medium clay; strong very coarse (> 50 mm) prismatic to lenticular structure; strong consistence dry; clear change to:
D	80 – 105+ cm	Yellowish brown (10YR5/6); sandy clay; apedal; strong consistence dry; becoming sandier with depth.

Key Profile Features:

Texture contrast between the surface (A1) horizon and subsoil (B21) horizon.
Strongly structured subsoils.

Soil Profile Characteristics:

-	pH	Salinity	Sodicity	Dispersion
Surface soil (A1 horizon)	Strongly Acid	Very Low	Non-sodic	None
Subsoil (B21 horizon)	Slightly Acid	Very Low	Non-sodic	Slight¹
Deeper subsoil (B22)	Slightly Alkaline	Very Low	Sodic	None

¹ Moderate after remoulding

Chemical and Physical Analysis:

Horizon	Horizon Depth (cm)	pH (water)	EC dS/m	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


A1	0-15	5.3	0.09	17	35	18	20	31.4	11.1
B21	15-45	6.1	<0.05	19	28.5	18	30	27.5	15.0
B22	45-80	7.7	0.13	22.5	31	16	26	26.0	14.4

Management Considerations

Whole profile

Plant available water is considered to be low, based on an effective rooting depth of 45 cm.

Surface (A) horizon

The surface soil is strongly acid. However, the level of exchangeable aluminium is quite low (<10 mg/kg) and is unlikely to affect the growth of aluminium sensitive species, particularly as the soil becomes alkaline with depth. 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.
Potassium levels are moderate and plant responses to potassium fertiliser is unlikely.
Salinity is not a problem in the surface soil.
Deficiencies of molybdenum and phosphorus may occur in the strongly acid surface soils and increasing the pH by lime application should enable the phosphorus (from superphosphate) and molybdenum to become more available.
The nutrient holding capacity of the surface (A1) horizon is moderate (based on the sum of the exchangeable calcium, magnesium, potassium and sodium cations).

Subsoil (B) horizons

The pH increases with depth allowing the successful growing of deep rooting aluminium sensitive species (e.g. lucerne).The coarse strong prismatic nature of the clay B horizon confines the roots to cracks and makes it difficult for the roots to fully exploit the soil (See photo opposite). The deep subsoil is also sodic and slakes considerably when wet.
The coarse strong prismatic nature of the clay B horizon confines the roots to cracks and makes it difficult for the roots to fully exploit the soil (See photo opposite). The deep subsoil is also sodic and slakes considerably when wet.

Soils and landforms of the Omeo/Benambra and Tambo Valley region - soil-landform unit Benambra EG204 profile2

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

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