Site IS24

Location: Haven

Australian Soil Classification: Calcic, Mottled-Mesonatric, Yellow SODOSOL

General Landscape Description: Dune slope on a Dunefield
Geology: Quaternary Lowan Formation: aeolian fine to medium grained dune sand

A1	0-15 cm	Dark greyish brown (10YR4/2) sandy loam; hardsetting surface condition; weak coarse granular structure; strong consistence dry; pH 6.7; sharp boundary to:
A2e	15-25 cm	Brown (10YR5/3) conspicuously bleached (10YR8/1d); sandy clay massive, (structureless) with cemented capping; very strong consistence dry; pH 7.5; sharp boundary to:
Subsoil
B21	25-60 cm	Light brown (7.5YR6/5) with (10YR6/3) mottles; light clay; subplastic; weak blocky structure; very few (<2%) hard calcareous segregations; pH 8.8; sharp boundary to:
B22	60-90 cm	Light brownish grey (2.5YR6/2); heavy clay; weak blocky structure; very few (<2%) hard calcareous segregations; pH 9.3; gradual boundary to:
B23	90-120 cm	Light brownish grey (2.5YR6/2); heavy clay; weak blocky structure; few (2-10%) hard calcareous segregations; pH 9.3.

• Strongly texture contrast profile, sodic.
• Plant available water capacity (PAWC) is considered to be relatively medium (estimated at 105 mm). This is based on available laboratory data and assumes an effective rooting depth of 60 cm. The strongly sodic deeper subsoil and increasing level of soluble salts will restrict rooting depth. The availability of moisture to the plant will depend on soil structure and consistence and will be most available in the more friable surface horizon. In dense and coarsely structured subsoils it is likely that there will be a large amount of unused ‘available’ moisture at depth in the subsoil.
• The strongly alkaline profile suggests that some nutrients (eg. iron, manganese, zinc, and copper) may be poorly available to plants and that deficiencies are likely to occur. Deficiencies can be determined by plant tissue analysis. The high alkalinity of the soil profile will reduce the potential of the soil to support some crops (eg. lupins).
• The surface soil is self-mulching which provides an ideal seed bed. In the dry to moist stage, these soils are friable and easy to work, but become sticky when wet. Crop establishment is promoted on friable surface soils compared to non-friable soil. Badawy (1981) notes, however, that cereal crops grown on friable clays are more prone to cereal cyst nematode.
• 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 will be relatively slow. After heavy rains, water can lie for long periods in the deeper gilgai depressions.
• The high wilting point value (ie. 23%) indicates that plants will be unable to utilise light rains when the soil is relatively dry.
• This soil has a high cation exchange capacity with relatively high levels of exchangeable calcium and potassium. These soils tend to mineralise nitrogen readily in cultivated bare fallows and initially produce high yields but total nitrogen levels diminish rapidly with cropping. On similar soils in the Wimmera, legumes (including subterranean clover) often respond to additions of zinc, molybdenum, manganese, sulphur and phosphorus. Cereals respond to additions of phosphorus and zinc (Badawy 1981).
• Tillage of cracking clay soils should be avoided if the soil is wet (ie. wetter than the plastic limit). At such moisture conditions, excessive tillage, trafficking or over-stocking could result in structural damage (eg. compaction, smearing occurring). Ideally, tillage should take place on clay soils such as these when the soil is drier than the plastic limit, down to at least the tillage depth. [See Appendix A for information on clay compaction (page A-20) and plastic limit (page A-31)].
• The upper subsoil is sodic but does not disperse. As a result, root and water movement into the subsoil may not be as restricted as for other soils with strongly dispersive subsoils. The high levels of exchangeable calcium will contribute to reducing dispersion. The calcium to magnesium ratio is still relatively high (2.6) in the upper subsoil.
• The deeper subsoil (from 60 cm depth) becomes strongly sodic and root and water movement is likely to be restricted at depth. The high level of exchangeable sodium in the subsoil may also result in nutrient imbalances and may even have a toxic effect on some plants. The levels of exchangeable magnesium also increase in the deeper subsoil resulting in a much-reduced calcium to magnesium ratio.
• The salinity rating becomes medium at 85 cm depth. This may restrict the growth of deeper rooted salt sensitive species. The subsoil displays strong vertic properties, which indicates that significant shrinking and swelling occurs with wetting and drying cycles. This may disturb the roots of some plant species and has engineering implications (eg. disturbance to building foundations and fence lines).
• The original gilgai microrelief is caused due to the vertic properties of the soil and resultant shrinking and swelling with alternate wetting and drying. This forces ‘blocks’ of soil material gradually upward to form mounds (or ‘puffs’). The soil on the mounds will be different to soils on the depressions. Mound soils tend to be lighter in colour and have higher carbonate contents. Salinity can also often be higher in the upper soil profile on the mounds. Continuous cultivation has resulted in the smoothing out of many of these gilgai formations. The forces that created them, however, are still operating as is evident by the displacement of fence posts; and if the land is left undisturbed over a number of wetting and drying seasons they will reform. In areas with gilgai microrelief, crop and pasture growth is likely to be uneven across a paddock due to soil variations and poor drainage conditions in depressions. Levelling of gilgais can reduce the depth of surface soil on gilgai mounds, which may expose the subsoils.