Site IS21

Location: Horsham

Morphological Soil Type: Bungalally Clay

Australian Soil Classification: Episodic-Endocalcareous, Epipedal, Grey VERTOSOL

Northcote Factual Key: Ug 5.24
Great Soil Group: grey clay
Mapping Unit: Bungalally Clay.


General Landscape Description: Lake and lunette plain.
Site Description: Cleared and cultivated area, seven kilometres south east of Horsham.
Geology: Late Pleistocene to Holocene, lacustrine deposition. Quaternary Coonambidgal Formation: fluvial to lacustrine clays and sands
Native Vegetation: Original vegetation probably Black Box (Eucalyptus largiflorens).

IS21 Landscape

Soil Profile Morphology:

Surface Soil

A1	0-20 cm	Dark grey (10YR4/1); light medium clay; subplastic; cracking and self-mulching surface condition; moderate angular blocky structure; very strong consistence dry, slightly sticky consistence wet; pH 7.5; sharp and smooth change to:	IS21 Profile
Subsoil
B21	20-30 cm	Dark grey (10YR4/1); light clay; subplastic; strong very coarse prismatic structure; strong consistence dry, slightly sticky consistence wet; pH 8.2:
B22	30-65 cm	Dark grey (10YR4/1); heavy clay; plastic; strong very coarse prismatic structure; strong consistence dry, slightly sticky consistence wet; pH 8.3; gradual change to:
B23	65-135 cm	Grey (10YR5/1); heavy clay; plastic; moderate angular blocky structure; very strong consistence dry, slightly sticky consistence wet; contains very few (< 2 %) hard carbonates; pH 8.5; gradual change to:
B24	135-190 cm	Grey (10YR5/1); medium clay; plastic; moderate angular blocky structure; very strong consistence dry, slightly sticky consistence wet; pH 9.2.

Key Profile Features:

• High clay content throughout soil profile.
• The soil cracks significantly when dry.
• Vertic properties (ie. significant shrink-swell characteristic).

Soil Profile Characteristics:

	pH	Salinity Rating	Sodicity	Dispersion
Surface (A1 horizon)	Slightly Alkaline	Low	Sodic	Slight1
Subsoil (B21 horizon)	Moderately Alkaline	Low	Sodic	Slight1
Deeper Subsoil (at 1 m)	Moderately Alkaline	Medium-High	Strongly Sodic	Strong

¹ Strong dispersion after remoulding.

The surface soil is slightly alkaline. The subsoil is moderately alkaline.

The salinity rating is low in the surface and upper subsoil becoming high with depth.

The surface and upper subsoil is sodic becoming strongly sodic with depth.

The clay content is high throughout the profile.

Horizon	Sample Depth cm	pH		EC dS/m	Sodium Chloride %	Exchangeable Calcium cmol-/kg	Exchangeable Magnesium cmol-/kg	Exchangeable Potassium cmol-/kg	Exchangeable Sodium cmol-/kg	Exchangeable Aluminium mg/kg	Exchangeable Acidity cmol-/kg	Field Capacity -30okPa	Permanent Wilting Point -1500okPa	Coarse Sand %	Fine Sand %	Silt %	Clay %
		H2O	CaCl2
A1	0–20	7.5	NA	0.19	0.02	19.8	10.5	3.5	2.6	NA	9.6	NA	30.2	1	11	5	81
B21	20–30	8.2	NA	0.2	0.02	20.6	11.5	3.5	5	NA	8.2	NA	35.5	1	5	5	87
B22	30–65	8.3	NA	0.41	0.07	19.1	11.3	3.5	6.5	NA	7.1	NA	33.7	1	7	3	86
B23	65–135	8.5	NA	0.88	0.18	13.9	12.8	3.5	8.8	NA	5.7	NA	33.5	1	8	4	87
B24	135–190	9.2	NA	1.03	0.21	NA	NA	NA	NA	NA	NA	NA	35.0	1	6	4	84

Note: NA=not assessed.

Management Considerations:

Whole Profile

• Plant available water capacity (PAWC) is considered to be moderate (estimated at 140 mm). This is based on available laboratory data and assumes an effective rooting depth of 65 cm. The effective rooting depth will be restricted in the strongly sodic deeper subsoil which has a medium to high salinity rating.

Surface (A) Horizon

• The surface soil is sodic and disperses strongly after remoulding. This indicates that structural degradation (eg. surface sealing, increased cloddiness) may occur if the soil is cultivated or overstocked in a moist to wet condition. Also, raindrop action on bare surface soil may also promote dispersion and result in surface sealing or surface crust formation. Surface cover should be maintained to protect against raindrop damage. The use of gypsum may assist in ameliorating the surface soil.
• When the soil is dry, heavy rains will move down soil cracks. This rapid recharge can be valuable for the survival of plants near wilting. When wet, the soil will swell and further infiltration of water will be relatively slow.
• Tillage of cracking clay soils should be avoided when the soil is wetter than the plastic limit. At such a moisture condition, excessive tillage, trafficking or overstocking may result in soil structural damage (eg. compaction, smearing) occurring. Ideally, tillage and trafficking should take place when the soil is drier than the plastic limit, down to at least the tillage depth.
• The high wilting point value (ie. 30 %) indicates that plants will be unable to utilise light rains when the soil is relatively dry.

Subsoil (B) Horizons

• The coarsely structured upper subsoil is sodic and disperses slightly. This is likely to restrict root and water movement somewhat. The relatively high level of exchangeable calcium relative to magnesium in the upper subsoil will probably have a beneficial effect on soil structure.
• Strong dispersion occurs in the upper subsoil after remoulding. This indicates that disturbance to this horizon during tillage when the soil is wet will result in structural degradation occurring.
• The level of soluble salts becomes medium to high in the deeper subsoil (from 65 cm depth). At these levels, the growth of salt sensitive species (eg. faba beans, linseed, chick peas, lupins) may be restricted.

Profile Described By: John Martin, Nabil Badawy, Ron Cawood, Geoff Pope, John Galea, John Turner (1970).

Reference: "Major Agricultural Soils of the Wimmera Irrigation Area". John Martin, Mark Imhof, Lourey Ruth, Rob Nink, Karen DePlater, Paul Rampant, Sonia Thompson, S. Alexander. Department of Natural Resources and Environment, Victoria. 1996.