SW8

Location: Alvie

Australian Soil Classification: Sodic, Eutrophic, Brown DERMOSOL

General Landscape Description: Lower slope of a gently undulating rise.
Geology: Quaternary volcanic ash deposits (Qvs).
Land Use: Pasture has been cultivated and improved. Alternate with silage crop. Irrigated in Summer.


SW8 Landscape

Soil Profile Morphology:

Surface Soil

A1	0-15 cm	Brown (7.5YR4/2); firm surface condition; fine sandy clay loam; moderate medium blocky, parting to moderate fine blocky structure; firm consistence moderately moist; pH 6.6; clear change to:	SW8 Profile
Subsoil
B21	15-25 cm	Dark reddish brown (5YR3/3); heavy clay loam (becoming light clay with depth); moderate medium blocky, parting to moderate fine polyhedral structure; firm consistence moderately moist; pH 6.5; abrupt change to:
B22	25-40 cm	Dark brown (7.5YR3/4); light medium clay; strong medium polyhedral, parting to strong fine polyhedral structure, smooth faced peds; very firm consistence dry; pH 6.5; gradual change to:
B23	40-50 cm	Dark brown (7.5YR3/2); medium clay; strong coarse blocky, parting to strong fine polyhedral structure; firm consistence slightly moist; roots to 50cm; pH 7.1; gradual change to:
B/C	50-70 cm	Dark brown (7.5YR3/2); fine sandy clay loam; very firm to strong consistence dry; contains a common (20%) amount of weathered basalt and volcanic ash; pH 8.0:
C	70+ cm	Volcanic ash deposits.

• Lack of strong texture contrast between surface (A) horizons and subsoil (B21) horizon.
• Moderately deep soil profile (ie. 70 cm) overlying volcanic ash deposits.

	pH	Salinity Rating	Sodicity	Dispersion
Surface (A1 horizon)	Slightly Acid	Low	Sodic	None
Subsoil (B21 horizon)	Slightly Acid	Very Low	Marginally Sodic	None
Deeper Subsoil (at 50-70 cm)	Moderately Alkaline	Moderate	Non-Sodic	None

The surface (A) horizons and upper subsoil are slightly acid. The deeper subsoil is slightly alkaline becoming moderately alkaline at depth.

The salinity rating is low to very low becoming moderate at depth.

The surface is sodic. The upper subsoil (15-25 cm depth) is only marginally sodic. Strong dispersion occurs after remoulding. The deeper subsoil is non-sodic and dispersion occurs after remoulding.

The clay percentage increases gradually down the profile but decreases in the B/C horizon when ash is mixed in.

Horizon	Horizon Depth (cm)	Organic Carbon %	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	0-15	2.4	16.1	7.0	34.8	21.0	30.0
B21	15-25	1.4	17.9	7.0	31.5	14.5	41.0
B22	25-40		24.6	6.7	21.8	11.0	53.5
B23	40-50		30.5	6.3	18.4	10.5	57.0
B/C	50-70		23.7	23.4	36.0	14.0	17.5

Management Considerations:

Whole Profile

• Plant available water capacity (PAWC) is considered to be low (estimated at 85 mm) for this soil profile. This is based on available laboratory data. Effective rooting depth will be restricted by the compacted ash deposits in the deeper subsoil. Most roots in the soil pit were observed to 50 cm depth.

• The inherent fertility (based on the sum of the exchangeable basic cations) of the surface horizons is moderate-high.
• The surface soil is reasonably well structured (parting to fine blocky structure) which should allow for good root proliferation.
• Due to the relatively high clay content in the surface horizon, such soils may be prone to compaction if excessively disturbed (eg. cultivation, trafficking) whilst in a moist-wet condition (ie wetter than the plastic limit).

• Although non-sodic, the upper subsoil disperses slightly (strongly after remoulding). Disturbance to this horizon by deep tillage (when in a moist to wet condition) may result in some structural degradation occurring.
• Exchangeable magnesium levels are high in the subsoil horizons (ie. > 45%). Values of exchangeable magnesium to Cation Exchange Capacity of over 20 % can induce potassium deficiency in some soils (Baker et al. 1993).