GP78

Location: Bushy Park.	Australian Soil Classification: Magnesic, Mottled-Mesonatric, Yellow SODOSOL
Great Soil Group: solodic	Geology: Pleistocene sediments (quartz gravel probably derived from Carboniferous sediments in uplands).
General Landscape Description: Gently undulating plain.	Mapping Unit: Briagolong
Site Description: Grazing paddock.

Site GP78 Landscape

Soil Profile Morphology:

Surface Soil			Site GP78 Profile
A1	0-10 cm	Dark brown (10YR3/3); fine sandy loam; weakly structured, very firm consistence dry; pH 5.1:
A2	10-25 cm	Brown (7.5YR5/4) bleached (7.5YR7/2); fine sandy loam; weak structure; very firm consistence dry; contains many (50%) quartz fragments (1-5 mm in size) and pebbles; pH 5.4; sharp change to:
Subsoil
B21	25-50 cm	Brownish yellow (10YR6/6); medium clay; moderate coarse prismatic, parting to moderate coarse blocky structure; strong consistence dry; pH 6.7:
B22	50-80 cm	Light olive brown (2.5Y5/4) with strong brown (7.5YR5/6) mottles; medium clay; moderate coarse prismatic, parting to moderate coarse blocky structure; strong consistence dry; pH 7.7
B23	80-130 cm	Yellowish brown (10YR5/6) with strong brown (7.5YR5/8) and grey (10YR6/1) mottles; light medium clay; moderate coarse prismatic parting to moderate coarse blocky structure; strong consistence dry; contains few (5-10%) manganese flecks; pH 8.0
B24	130+ cm	Light grey (10YR7/1) with strong brown (7.5YR5/8) mottles; contains many (30%) rounded quartz pebbles (3-5 mm in size). Iron cemented river gravels occur from 150 cm depth

Key Profile Features:

Strong texture contrast between surface (A) and subsoil (B21) horizons.
Conspicuously bleached subsurface (A2) horizon.
Contains many (50%) quartz pebbles in the subsurface (A2) horizon.

Soil Profile Characteristics:

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

	The soil profile becomes increasingly alkaline with depth.		The surface soil is non-sodic. The subsoil is strongly sodic throughout.
	The surface salinity rating is moderate. The subsoil rating is low.		The clay content increases significantly at the A/B horizon interface.

Horizon	Horizon Depth (cm)	pH (water)	pH (CaCl₂)	EC 1:5	NaCl	Exchangeable Cations
						Ca	Mg	K	Na
						meq/100g
A1	0-10	5.1	4.5	0.32		3.1	1.1	0.5	0.1
A2	10-25	5.4	4.6	0.13		0.72	0.44	0.47	0.3
B21	25-50	6.7	5.7	0.19		0.82	11	0.47	2.5
B22	50-80	7.7	6.6	0.25		0.2	9.2	9.2	3.4
B23	80-130	8	6.8	0.25		0.2	8.5	0.2	3.5
B24	130+

Horizon	Horizon Depth (cm)	Exchangeable Aluminium mg/kg	Exchangeable Acidity meq/100g	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	0-10	<10			5.1	23	46	18	9
A2	10-25	11			2.6	27	48	17	7
B21	25-50				17.7	10	26	15	48
B22	50-80				14.7	8	29	19	42
B23	80-130
B24	130+

Management Considerations:

Whole Profile

Plant Available Water Capacity (PAWC) is considered to be quite low (estimated at 27 mm) for this soil profile. This is based on an estimated effective rooting depth of 25 cm (i.e. surface soil). The dense and coarsely structured upper subsoil is likely to restrict rooting depth. Most of the plant available water will be in the surface (A1) horizon as water storage is more limited in the stony A2 horizon. 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 strongly acid. This indicates that aluminium toxicity could occur. However, the level of exchangeable aluminium measured at this site is very low (<10 mg/kg). These levels are unlikely to affect plant growth. A pH/aluminium test on a bulked sample (from across the paddock) would be most appropriate, however, to determine if lime is needed to raise soil pH
Manganese toxicity may also occur in strongly acid soils, particularly if poorly drained (as waterlogging may bring manganese into solution)
Deficiencies in molybdenum, potassium and phosphorus may also occur in the strongly acid and sandy surface soil. If lime is needed to raise soil pH then this should result in increased nutrient availability
The level of soluble salts in the surface is moderate to high and may restrict the growth of salt sensitive species. These levels may be unnaturally high due to the effects of the dry season at the time of sampling (i.e. summer 1997) and are likely to decline to more natural levels following periods of irrigation or heavy rainfall
The surface (A1) horizon has a low nutrient holding capacity (based on the sum of the exchangeable calcium, magnesium and potassium cations). Organic matter is important for maintaining soil fertility, water holding capacity and enhancing surface soil structure; especially in soils such as these with high fine sand contents
The low wilting point value (i.e. 5%) of the surface (A1) horizon indicates that plants will be able to utilise very light rains when the soil is dry. However, due to the low water storage capacity, plants will soon suffer moisture stress unless further rainfall occurs
The presence of a conspicuously bleached subsurface (A2) horizon indicates that periodic waterlogging occurs above the more slowly permeable subsoil. This horizon also has a very low inherent fertility and will become ‘spewy’ when wet

Subsoil (B) Horizons

The dense and coarsely structured subsoil is strongly sodic and disperses completely. This will result in significantly restricted root and water movement into the subsoil. The use of gypsum in association with deep ripping has been advocated by some researchers as an effective way to ameliorate sodic subsoils, but this may not be an economic option. Deep ripping should not be carried out when the subsoil is in a moist to wet condition
The low exchangeable calcium to magnesium ratio (0.1) in the subsoil indicates that some nutrient imbalances (eg. calcium deficiency) could occur

Profile Described By: Mark Imhof, Ian Sargeant (22/4/98).

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