Site MP24

Group: Birchip Cropping Group

Australian Soil Classification: Episodic-Epicalcareous, Self-mulching, Brown VERTOSOL

General Landscape Description: Level alluvial plain within the Tyrell Creek Land System (Rowan and Downes, 1963).

Site MP24 Landscape

Soil Profile Morphology:

Surface Soil

A1	0-10 cm	Dark brown (10YR4/3); light clay; self-mulching surface condition, friable consistence dry; surface cracking evident; pH 7.9:	Site MP24 Profile
Subsoil
B21	10-30 cm	Dark brown (10YR4/3); medium clay (subplastic); moderate prismatic, parting to strong very fine blocky structure; pH 8.9:
B22k	30-55 cm	Brown (10YR5/3); light medium clay; very coarse prismatic, parting to strong medium to fine blocky structure; very firm to strong consistence dry; contains few (2-10%) fine earth carbonates; pH 9.1; sharp change to:
B23	55-100 cm	Light yellowish brown (10YR6/4); light medium clay; structure similar to above; strong consistence dry; pH 9.0; gradual change to:
B24	100-180 cm	Light medium clay; with soft manganese segregations in the 160 -180 cm zone; pH 9.1.

Soil Profile Characteristics:

	pH	Salinity Rating	Sodicity	Dispersion
Surface (A1 horizon)	slightly alkaline	very low	sodic	none1
Upper Subsoil (B21 horizon)	strongly alkaline	medium	strongly sodic	moderate
Deeper subsoil (at 1 m)	very strongly alkaline	very high	very strongly sodic	none2

¹ Dispersion occurs after remoulding. ² Due to a high level of soluble salts.

Horizon	Horizon Depth (cm)	pH (water)	pH (CaCl2)	EC ds/m	NaCI %	Exchangeable Cations				Field Capacity pF 2.5	Wilting Point pF 4.2	Coarse Sand (0.2 - 2.0 mm)	Fine Sand (0.02 -0.2 mm)	Silt (0.002 -0.02 mm)	Clay (<0.002 mm)
						Ca	Mg	K	Na
						meq/100g
A1	0-10	7.9	7	0.13		20.6	6.6	2.4	1.9	44	25	11	14	8	60
B2	10-30	8.9	8	0.67	0.08	16.2	11.3	2.2	12.8	57	35	5	6	28	48
B22	30-55	9.1	8.6	2.5	0.47	8.6	12.4	2	22.7	59	35
B23	55-100	9	8.6	3.78	0.76	7.7	12.8	1.7	23.9	53	26
B24	100-180	9.1	8.7	2.7	0.54	7	12.2	1.4	22.3

Management Considerations:

Surface (A) Horizon

• Tillage or excessive trafficking of cracking clay soils should be avoided if the soil is very moist to wet (i.e. wetter than the plastic limit). At such moisture conditions, tillage or excessive trafficking can result in structural damage (e.g. 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 (25%) indicates that plants will be unable to utilise light rains falling on relatively dry soil.

Subsoil (B) Horizons

• The upper subsoil is strongly sodic and dispersive. This will result in root and water movement being significantly restricted. The deeper subsoil below 30 cm depth becomes extremely sodic (and has a low exchangeable calcium to magnesium ratio) which will have a deleterious effect on soil structure and may create adverse chemical conditions for some plants.

• The level of soluble salts is medium in the upper subsoil (i.e. 10-30 cm depth). This may affect the growth of salt sensitive species (e.g. chick peas, lupins). The salinity rating becomes very high from 30 cm depth and the growth of a number of plant species (possibly including wheat, oats and barley) may be significantly restricted.

• The subsoil is strongly to very strongly alkaline throughout. This indicates that phosphorus and trace elements such as iron, manganese, copper and zinc may be poorly available to plants.

Profile Described By: Mark Imhof and John Martin (23/1/93).

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