Calcarosols

Calcarosols lack strong texture contrast between surface (A) and subsoil (B) horizons. These soils are also calcareous throughout and often have accumulations of calcium carbonate (lime) in the soil profile. These soils form on calcareous, aeolian sediments of variable texture.

In the Mallee, Calcarosols generally have a small, gradual increase in clay content with depth. Lime is abundant in the subsoils, either in soft form, in nodules or as blocks, and it may extend to the surface of medium to heavy textured soils. The pH tends to be highly alkaline. However, the upper horizons in sands may only be weakly alkaline. Sodicity and salinity levels are usually high in the heavier subsoils.

Dune and swale landscape near Walpeup.

Calcarosols in the Mallee Region. This map of Calcarosols in the Mallee region has been developed by Jim Rowan and is based on the Land Systems of Victoria (1:250 000). It shows areas where Calcarosols are most likely to occur within the region and should only be used as a general indication of their distribution. Please note that other soil types may also occur within these mapped areas. Calcarosols may occur in areas not mapped here, however, these are most likely to be minor occurrences.

Mallee Calcarosols

A sandy Calcarosol associated with a dune near Waleup.

The Calcarosols in the Mallee region vary quite considerably in terms of soil texture - ranging from those dominated by sands to those that are clayey throughout. Soil texture has a big influence on the agronomic performance of the land. Sands are easily worked, but they have low fertility reserves and are very prone to wind erosion. Heavier textured soils are more fertile and less erodible, but more prone to salting and hardsetting when over-cultivated.

A Calcarosol associated with swales near Walpeup. These soils have a sandy loam surface.

A Calcarosol near Birchip. This soil has a light clay surface that grades to medium to heavy clay.

Three kinds of Calcarosols are shown on the map - light textured, heavy textured and stony. Light textured Calcarosols predominate in the north of the region. Here east-west dunes alternate with broad swales. The soils in the swales and broad north-south trending ridges generally have loamy surfaces overlying clay subsoils that are often sodic. Sands are most common on the east-west dunes. The sands are fairly closely spaced on the farmlands in the central Mallee, and the different agronomic requirements of the dunes and intervening loamy flats can pose difficulties for management. Heavy textured Calcarosols predominate in the south of the region where east-west dunes are infrequent or replaced by sub-round hummocks. Soils on the upper hummock and stranded ridge (see Geology and Geomorphology) crest and upper slopes have loamy surfaces. The lower slopes and plains have a clay loam to light clay surface and these may grade into Vertosols. These heavier textured soils are usually gilgaied on the plains and ridge slopes. Sands occur on the occasional east-west dunes further north (see Geology and Geomorphology). The heavier lands are relatively productive and stable.

A shallow Calcarosol overlying hard calcrete material near Walpeup.

Stony Calcarosols generally have loamy horizons that may or may not contain visible lime. At shallow depth, usually within 30 cm of the soil surface, there is a solid limestone layer a metre or more thick which is thought to have formed from old aeolian deposits. On cultivated soils a litter of limestone blocks occur, that reduce wind erosion but cause wear and tear on machinery. Water holding capacities are reduced by stone content and shallow soil depth. Stony soils predominate on loamy agricultural areas in the western Mallee. They are particularly widespread further west in South Australia. The area mapped in the very north-west corner of the Mallee appears to be dominated by stony soils. They are also widespread between Murrayville and Underbool but are discontinuous and not easily detected on conventional aerial imagery. These occurrences are not shown on the map. Occurrences decrease towards the east.