PPW8

Location: Werribee - Research Farm
Aust. Soil Class.: Vertic (& Sodic), Calcic, Brown DERMOSOL / Vertic, Mottled-Mesonatric, Grey SODOSOL
Northcote Factual Key:: Ug 5.25
Great Soil Group:: solodic
Previous Soil Type (Skene 1954): Austral clay loam (depressions at junction of basalt and alluvial deposits)
Maher and Martin (1979) map unit: 8/7
General Landscape Description: Level plain.
Site Description: Grazing paddock.
Geology: Quaternary alluvial (prior stream) and aeolian deposits/Quaternary basalt.

WP5 Landscape

Soil Profile Morphology

Surface Soil			PPW8 Profile
A1	0-5 cm	Dark brown (10YR3/3); heavy clay loam (fine sandy); hardsetting surface condition; very firm consistence (dry); many roots present; pH 5.2; clear change to:
Subsoil
B21	5-30 cm	Dark yellowish brown (10YR4/4) with yellowish brown (10YR5/6) mottles; medium clay; strong coarse-medium blocky structure; strong consistence (dry); pH 5.9:
B22	30-60 cm	Light olive brown (2.5Y5/4 and 5/6); medium heavy clay; strong coarse blocky structure; strong cracking when dry; very strong consistence (dry); pH 7.7:
B23	60-80 cm	Light yellowish brown (2.5Y6/4); medium heavy clay; very strong consistence (slightly moist); few (5%) medium calcareous nodules (2-5 mm); few roots; pH 8.9:
B24	80-120 cm	Yellowish red (5YR5/6 & 5/8); medium clay; very strong consistence (slightly moist); few (5%) fine calcareous nodules and few (2 %) basalt fragments (2-5 cm); pH 8.8:
B25k	120-140 cm	Yellowish red (5YR5/6); medium clay; many (20 %) fine calcareous nodules and very few (2 %) basalt fragments; pH 8.9.

Note: In some areas, a discontinuous bleached subsurface horizon of variable depth (up to 50 cm) is present. This horizon is yellowish brown; conspicuously bleached (10YR 7/3 dry); very fine sandy clay loam with some rusty root channel mottling. This bleached horizon overlies a greyish brown (2.5Y 5/2) with light olive brown (2.5Y5/6) mottles heavy clay subsoil (B21) horizon. At depth, the subsoil becomes light olive brown (2.5Y 5/4), before becoming yellowish red (5YR 5/6) at 90 cm depth. This soil profile variation is related to the original gilgai microrelief.

Key Profile Features

• Soil profile variation related to gilgai microrelief (e.g. variable presence of bleached subsurface horizon, depth to subsoil clay horizons).

Soil Profile Characteristics

	pH	Salinity Rating	Sodicity	Dispersion
Surface (A1 horizon)	Strongly Acid	Low	Non-Sodic	None
Subsoil (B21 horizon)	Moderately Acid	Low	Sodic	None1
Deeper subsoil (at 120-140 cm)	Strongly Alkaline	Very High	Strongly Sodic	None2
1Moderate to strong dispersion after remoulding. 2Slight dispersion after remoulding. Lack of dispersion likely due to high level of soluble salts deeper in the soil profile.

Horizon	Horizon Depth (cm)	pH (water)	pH CaCl2	EC dS/m	NaCl %	Exchangeable Cations				Boron (CaCl2) mg/kg	Ex Al mg/kg	Ex Ac meq/100g	Field pF2.5	Wilting Point pF4.2	Coarse Sand (0.2-2.0mm)	Fine Sand (0.02-0.2mm)	Silt (0.002-0.02mm)	Clay (<0.002mm)
						Ca	Mg	K	Na
						meq/100g
A1	0-5	5.2	4.8	0.38	0.03	7.0	3.4	2.5	0.3		<10	15	38.2	16.7	12	25	19	31
B21	5-30	5.9	5.3	0.17		6.4	6.8	0.82	1.1		<10	11	29.8	16.9	3	31	20	43
B22	30-60	7.7	6.9	0.27	0.04	9.4	14	1.2	4.2				44.8	23.3	3	21	20	54
B23	60-80	8.9	8.3	0.7	0.09	8.5	16	1.2	5.8	5.5			51.7	21.5	3	20	19	50
B24	80-120	8.8	8.4	1	0.15	6.3	19	1.4	7.7	15			-	24.8
B25k	120-140	8.9	8.5	1.1	0.15	6.3	20	1.5	8.6	15

	<2µm Clay Mineralogy
Horizon	Depth cm	Quartz	Mica/Illite	Kaolin	Goethite	Orthclase	Smectite
B22	30-60	6	23	34	-	<1	37
B24	80-120	5	26	38	-	<1	32

2µm Cation Exchange Capacity
Horizon	Depth cm	SiO2 %	Al2O3 %	MgO %	P2O5 %	K2O %	TiO2 %	MnO %	Fe2O3 %	BaO %	Sum %	CEC cmol/kg
B22	30-60	48.7	22.8	1.2	0.4	2.0	1.2	0.0	9.2	3.7	89.1	49
B24	80-120	48.5	22.6	1.4	0.3	2.0	1.0	0.0	10.1	3.9	89.9	52

Management Considerations:

Whole Profile

• There is likely to be a variation in soil properties across the paddock due to gilgai microrelief (e.g. depth of bleached subsurface horizon, depth to sodic clay). Variations in paddock performance may be encountered as a result.
• Management strategies for all soils should aim to increase organic matter levels in the surface soil; minimise the degradation of soil aggregates and porosity; promote the development o stable biopores; improve the calcium status of the cation exchange complex - particularly when sodium is a significant part (e.g. applying gypsum), and break up any hardpans. Less frequent tillage; using less aggressive implements, and working the soil at optimum moisture content can all assist in maintaining soil aggregation and porosity as well as reducing the breakdown of organic matter.

Surface (A) Horizons

• The surface soil is strongly acid. As a result, deficiencies in molybdenum, potassium and phosphorus may occur. Manganese toxicity may also occur in strongly acid soils, particularly when poorly drained (as waterlogging may bring manganese into solution). Aluminium can become toxic in strongly acid soils. However, the exchangeable aluminium levels measured in the laboratory for this site are low. Raising the pH levels of acid soils by liming will help reduce the level of exchangeable aluminium. A lime test (samples across the whole paddock) may be appropriate to determine the amount of lime needed to raise pH. Other factors need to be considered, however, before lime is recommended (e.g. species growth, method of application, long trial response, likely cost benefit).

Subsoil (B) Horizons

• The coarsely structured subsoil is sodic (apart from the upper part in some areas) - and disperses after remoulding. This will provide some restriction to root and water movement into the profile.
• The level of soluble salts becomes high from 80 cm depth. This is likely to restrict the growth of deeper-rooted salt-sensitive species.
• Boron levels are quite high (> 15 mg/kg) in the deeper strongly alkaline subsoil (i.e. from 80 cm depth). This may affect deeper-rooted boron sensitive species.

Notes
Soil profile described by Mark Imhof and Siggy Engleitner (30 April, 2004).