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Site LP110

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Groups: Timor West Landcare Group
Aust. Soil Class.: Vertic (& Hypercalcic), Subnatric, Brown SODOSOL

General Site Description: Level plain.
Geology: Near boundary of Ordovician marine sediments and Quaternary alluvial sediments (Shepparton Formation).

Site LP110 Soil Landscape

Soil Profile Morphology:

Surface Soil			Site LP110 Soil Profile
A1	0-7 cm	Dark brown (10YR3/3); fine sandy clay loam (heavy); moderate coarse blocky structure; surface cracks; strong consistence (dry); very few (2%) ferruginous nodules (av. 5 mm diameter); pH 6.6; clear change to:
A21	7-15 cm	Dark yellowish brown (10YR3/4); fine sandy clay loam (heavy); moderate coarse blocky structure; strong consistence (dry); very few (2%) ferruginous nodules (av. 5 mm diameter); pH 7.1; sharp change to:
A2j	15-25 cm	(discontinuous) Yellowish brown (10YR5/6) sporadically bleached; fine sandy clay loam; very firm consistence (moderately moist); many (20%) ferruginous nodules (av. 6 mm diameter); pH 7.9; abrupt change to:
Subsoil
B21	25-50 cm	Dark yellowish brown (10YR4/4); medium heavy clay; moderate coarse blocky structure; firm consistence (moist); very few (2%) ferruginous nodules (av. 5 mm diameter); pH 8.5; clear change to:
B22	50-70 cm	Strong brown (7.5YR4/6); medium heavy clay; weak to moderate coarse blocky structure; slickensides present; firm consistence (moist); very few (2%) ferruginous nodules (av. 5 mm diameter); pH 8.6; wavy and gradual change to:
B23	70-140 cm	Dark yellowish brown (10YR4/4); medium clay; moderate medium sized blocky structure, parting to strong fine polyhedral structure; slickensides present; firm consistence (moist); many (30%) fine-earth carbonates; very few (2%) ferruginous nodules (av. 5 mm diameter); manganese stains and nodules at depth; pH 8.9.

Key Profile Features:

• Discontinuous and bleached subsurface (A2) horizon.
• Strong texture contrast between surface (A) horizons and the upper subsoil (B21) horizon.

Soil Profile Characteristics:

	pH	Salinity Rating	Sodicity	Dispersion
Surface (A1 horizon)	Slightly acid	Very low	Marginally Sodic	None 1
Subsoil (B21 horizon)	Moderately alkaline	Very low	Sodic	Strong
Deeper subsoil (at 140 cm)	Stongly alkaline	High	Strongly Sodic	None2

¹ Strong dispersion when remoulded. ² Lack of dispersion likely to be due to high level of soluble salts.

Horizon	Horizon Depth	pH (water)	pH CaCl2	EC dS/m	NaCl %	Exchangeable Cations				Ex Al mg/kg	Ex Ac meq/100g	Field pF2.5	Wilting Point pF4.2	Coarse Sand (0.2-2.0mm)	Fine Sand (0.02-0.2mm)	Silt (0.002-0.02mm)	Clay (<0.002mm)
						Ca	Mg	K	Na
						meq/100g
A1	0-7	6.6	5.4	0.09		5.6	6.3	0.88	0.74			13.3	26.2	8	42	19	30
A21	7-15	7.1	5.9	0.08		6.1	6.8	0.68	0.99			12.8	24.6	9	43	19	30
A2j	15-25	7.9	6.5	0.07		3.7	5.1	0.42	0.85			9	21.4	13	48	16	23.5
B21	25-50	8.5	7.3	0.22		7.3	21	1.1	4.3			24.9	44.4	4	26	11	58
B22	50-70	8.6	7.9	0.72	0.14	5.5	19	1.3	5.8
B23	70-140	8.9	8.4	1.12	0.19	17	21	1.2	6.9

Management Considerations:

Whole Profile

• Management strategies for all soils should aim to increase organic matter levels in the surface soil; minimise the degradation of soil aggregates and porosity; promote the development of stable biopores; improve the calcium status of the cation complex (when sodium is a significant part – i.e. sodic) and break up any hardpans. Less frequent tillage, using less aggressive implements, and working the soil at optimum moisture contents can all assist in maintaining soil aggregation and porosity as well as reducing the breakdown of organic matter.
• Plant available water capacity (PAWC) is estimated to be low (estimated at 70 mm) for this profile. This is based on the available laboratory data and an effective rooting depth estimated to be 60 cm. Effective rooting depth will be restricted by the strongly sodic subsoil and high level of soluble salts.

Whole Profile

• Values of exchangeable magnesium are greater than 48% throughout the soil profile and may have a toxic effect at depth (up to 64% with depth). Such levels in some soils may induce potassium deficiency (Baker and Eldershaw, 1993).

Surface (A) Horizons

• The surface (A) horizons have a moderate inherent fertility, which is beneficial for plant growth. Organic matter will be important for enhancing fertility
• The level of the organic carbon indicates that the organic matter of the surface soil is low. Organic matter is important for reducing slaking and enhancing soil aggregation, fertility and water holding capacity. It is also important for sandy surface soils (50% sand) to help build up the soils and reduce erosion risk. Organic matter levels will build up under pasture but will decline if cultivation takes place. Practices such as residue retention, minimum tillage and including pasture rotations should be utilised if cropping occurs.
• The surface horizons are dispersive after remoulding. This indicates that surface soil will disperse when worked in a moist condition even though it may not disperse in its natural state. The action of rain impact on the soil surface may also cause dispersion. By maintaining some pasture or stubble cover this may be prevented. Tillage or over-stocking of the soil should be avoided if the soil is moist to wet.
• The bleached subsurface (A2) horizon indicates that periodic waterlogging occurs on top of the more slowly permeable subsoil. This horizon is likely to become “spewy” as a result.

Subsoil (B) Horizons

• The dense and coarsely structured subsoil is sodic and strongly dispersive - becoming stongly sodic at 50 cm depth. This will result in restricted root and water movement in the subsoil. Water is likely to build up after heavy rains causing waterlogging.
• The level of soluble salts from 50 cm depth may affect the growth of salt sensitive species.
• The subsoil is strongly alkaline at 80 cm. This may affect some deep root plant species as some nutrients (e.g. copper, iron, manganese and zinc) may become poorly available to plants.
• The subsoil displays vertic properties (i.e. slickensides and deep cracking) which indicates that significant shrinking and swelling occurs in the deeper subsoil. This may have implications for engineering purposes (e.g. disturbance to fencelines, foundations).

Profile Described By: Mark Imhof,

References:

Baker, D.E. and Eldershaw, V.J. (1993). Interpreting Soil Analysis for Agricultural Land Use in Queensland. Project Report Series. Queensland, Department of Primary Industries.