Site LWA 20

Location: Birchip

Australian Soil Classification: Vertic (& Epihypersodic), Pedal, Hypocalcic CALCAROSOL (clayey surface texture)

General Landscape Description: Level Plain
Site Description: Cultivation paddock of demonstration site
Geology: Quaternary aeolian and alluvial deposits

LWA20 Landscape

Soil Profile Morphology:

Surface Soil

A1	0-10cm	Brown (7.5YR4/6); light clay; weak (10-20 mm) angular blocky structure, parting to moderate fine (5-10 mm) polyhedral structure; firm consistence (moderately moist); moderately calcareous effervescence of fine earth; abrupt change to:	LWA20 Profile
Subsoil
B21	10-35 cm	Brown (7.5YR5/4) with black (7.5YR2.5/1) mottles; light-medium clay; moderate medium (10-20 mm) sub-angular blocky structure; firm consistence (moderately moist); moderately calcareous effervescence of fine earth; clear change to:
B22	35-70 cm	Brown (7.5YR5/4) with black (7.5YR4/2) mottles; medium clay; strong coarse (50-100 mm) prismatic, parting to strong coarse (20-50 mm) sub-angular blocky structure; very firm consistence (dry); very few (<2%) soft calcareous segregations with very few (<2%) soft manganiferous segregations; gradual change to:
B23	70-100 cm	Brown (10YR5/3); medium clay; weak (50-100 mm) prismatic structure, parting to moderate coarse (20-50 mm) angular blocky structure; weak consistence (moderately moist); very few (<2%) soft calcareous segregations; distinct slickensides common; diffuse change to:
B24	100-140 cm	Light olive brown (2.5Y5/3) with olive grey (5Y5/2) mottles; medium-heavy clay; weak coarse (50-100 mm) prismatic, parting to moderate coarse (20-50 mm) angular blocky structure; weak consistence (moderately moist); slight calcareous effervescence of fine earth; distinct slickensides common.

Key Profile Features:

Gradual increase in texture (i.e. clay content) with depth down the soil profile.
Calcareous throughout soil profile.

Soil Profile Characteristics:

¹ slight to moderate dispersion after remoulding
² slight dispersion after remoulding

Management Considerations:

Whole Profile

In general, 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 ion exchange complex (particularly when sodium is a significant part) and break up any hardpans. Less frequent tillage, using less aggressive implements and working the soil at optimum moisture conditions can all assist in maintaining soil aggregation and porosity, as well as, reducing the breakdown of organic matter.The soil profile is strongly to extremely alkaline throughout. This indicates that phosphorus and trace elements such as iron, manganese, copper and zinc may be poorly available to plants.

Surface (A) Horizon

Tillage of clayey soils like these should be avoided if the soil is wet (i.e. wetter than the plastic limit). At such moisture conditions, excessive tillage, trafficking or over-stocking could result in some structural damage (e.g. compaction). Ideally, tillage should take place on clayey soils when the soil is drier than the plastic limit – down to at least the tillage depth.The surface soil is marginally sodic and some dispersion was noted in the field after the soil was remoulded. This indicates that some structural degradation (e.g. surface sealing, crusting, increased cloddiness) may occur if the soil is cultivated or overstocked in a moist to wet condition. Also, raindrop impact on bare surface soil may also promote dispersion and result in surface sealing. Surface cover should be maintained to protect the soil against raindrop action. Management practices such as minimum tillage, stubble retention and pasture rotation can be used to improve organic matter levels.

Subsoil (B) Horizons

Boron levels are quite high throughout the very strongly alkaline subsoil (for the mound components of the gilgai microrelief). These levels are likely to affect the growth of boron-sensitive species (including cereals, pulses, pasture legumes) where concentrations as low as 10 ppm, for example, can reduce lentil yield. Limited data estimates that the threshold level of soluble boron for cereals is 15 mg/kg (Cartwright et al., 1984). Other work at Victorian Institute Dryland Agriculture (VIDA) indicates that where there are low levels of soluble salts, boron tolerance can be comparatively high, with little reduction in wheat yield at levels of up to 45 ppm (Quinlan, 2001).The coarsely structured subsoil is strongly sodic – indicating that root and water movement into the subsoil are likely to be restricted.
The subsoil has a high level of soluble salts throughout – which is likely to significantly restrict the growth of salt-sensitive species. The high soluble salt levels are also likely to explain why dispersion is only slight in the strongly sodic subsoil – which suggests that subsoil permeability will not be as restricted as for similar non-saline sodic soils in the region.

Notes