GP31

Location: Macalister Research Farm.	Australian Soil Classification: Vertic & Hypocalcic, Subnatric, Brown SODOSOL.
Great Soil Group: Solodic.	Geology: Late Pleistocene fluvial sediments.
General Landscape Description: Level plain.	Mapping Unit: Denison.
Site Description: Dairy grazing paddock.

Site GP31 Landscape

Soil Profile Morphology:

Surface Soil			Site GP31 Profile
A1	0-25 cm	Dark greyish brown (10YR4/2); very fine sandy clay loam; very firm consistence dry; pH 6.0; clear change to:
A2	25-35cm	Yellowish brown (10YR5/4) conspicuously bleached; clay loam; contains a few (5%) iron nodules; pH 6.1; clear and wavy change to:
Subsoil
B21	35-60 cm	Strong brown (7.5YR5/6) with greyish brown (7.5YR5/2) mottles; light medium clay; moderate coarse blocky, parting to moderate fine polyhedral structure; friable consistence moist; contains a few (5%) manganese nodules (2-4 mm in size); pH 7.1; gradual and wavy change to:
B22	60-110 cm	Brown (7.5YR5/4); medium heavy clay; slickensides present; contains a few (5%) carbonate/silica nodules (up to 10 cm in size); pH 8.5:
B23	110+ cm	Weak red (2.5YR5/4) with slight strong brown (7.5YR5/8) mottles; medium clay; moderate coarse prismatic, parting to strong coarse blocky structure; strong consistence dry; pH 9.0.

Key Profile Features:

• Strong texture contrast between surface (A) horizon (27% clay) and the sodic subsoil (B21) horizon (60% clay).
• Vertic properties (i.e. significant shrink-swell characteristics) in deeper subsoil.

Soil Profile Characteristics:

Horizon	pH	Salinity Rating	Sodicity	Dispersion
Surface (A1 horizon)	Moderately Acid	Very Low	Non-Sodic	None1
Subsoil (B21 horizon)	Slightly Alkaline	Very Low - Low	Sodic	Slight2
Deeper subsoil (at 1 m)	Moderately Alkaline	Very Low - Low	Sodic	Complete

¹ Slight dispersion after remoulding.
² Complete dispersion after remoulding.

	The soil profile becomes increasingly alkaline with depth.		The surface is non-sodic. The subsoil is sodic throughout.
	The salinity rating is very low throughout the profile.		There is a sharp increase in clay at the A/B horizon interface.

Horizon	Horizon Depth (cm)	pH (water)	pH (CaCl2)	EC 1:5	Exchangeable Cations
					Ca	Mg	K	Na
					meq/100g
A1	0-25	6	5.2	0.06	3.8	1.5	0.25	0.26
A2	25-35	6.1	5.2	0.08	2	2	0.38	0.36
B21	35-60	7.1	6.1	0.11	2.8	7	0.44	1.3
B22	60-110	8.5	7.6	0.21	2.8	8.2	0.4	2
B23	110+	9	8	0.2	2	6.6	0.3	2.4

Horizon	Horizon Depth (cm)	Field Capacity pF2.5	Wilting Point pF4.2	Coarse Sand (0.2-2.0 mm)	Fine Sand (0.02-0.2 mm)	Silt (0.002-0.02 mm)	Clay (<0.002 mm)
A1	0-25	28	10	2	21	48	27
A2	25-35	26	11	4	19	44	33
B21	35-60	33	19	3	9	28	60
B22	60-110	32	19	1	5	33	61
B23	110+	34	21	1	6	39	54

Management Considerations:

Whole Profile

• Plant Available Water Capacity (PAWC) is considered to be moderate (estimated at 85 mm) for this soil profile. This is based on an estimated effective rooting depth of 60 cm (i.e. surface soil and upper subsoil horizons). The dense and coarsely structured deeper subsoil is likely to restrict rooting depth. The upper subsoil is well structured and friable when moist so it is likely to be suitable for root growth. Most of the plant available water (i.e. 60 mm) will be in the surface (A) horizons. PAWC has been estimated using a model developed by Littleboy (1995) which uses analytical data for clay%, silt%, fine sand%, coarse sand % and wilting point.

Surface (A) Horizons

• The surface soil is non-sodic and does not disperse. However, slight dispersion occurs after remoulding indicating that some structural degradation may occur if cultivation or overstocking occurs when the soil is wet.
• The presence of conspicuous bleaching in the subsurface (A2) horizons indicates that periodic waterlogging occurs above the slowly permeable subsoil.

Subsoil (B) Horizons

• Root and water movement into the subsoil will be restricted to some degree by the sodic and slightly dispersive clay subsoil. The upper subsoil horizon is, however, reasonably well structured (parting to fine sized polyhedral shaped peds) and is fairly friable when moist. Root growth is therefore likely to be less restricted in subsoils such as this, compared to the denser and coarsely structured subsoils in the region.
• The subsoil displays vertic properties (i.e. slickensides evident) which indicates that significant shrinking and swelling occurs during wetting and drying cycles. This may disturb the roots of some plants and may have some engineering implications (e.g. disturbance to fence lines).

Profile Described By: Mark Imhof, Ian Sargeant (19/12/96).