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Soils

By Robert Karfs, NT Department of Infrastructure, Planning and Environment.
From Managing for healthy country in the VRD, published by Tropical Savannas CRC, Darwin 2000.

Catchments in the VRD

Five main catchments now drain the Victoria River District. The Victoria River is the largest of these and empties into the Joseph Bonaparte Gulf. Other coastal draining catchments are associated with the Keep, Fitzmaurice and Ord Rivers. The remaining catchment drains southwards into the desert and is associated with the Sturt, Hookers and Winnecke Creeks. Most of the coastal flowing rivers maintain waterholes that persist throughout the dry season, while the persistence of many intermittent waterholes is dependent on the previous wet season's rainfall.

Soil types

In the VRD, a clear relationship exists between soil type and climate, drainage and parent material.

Well-drained, steep hilly country with rock outcrops tends to have shallow skeletal soils. Deeper soils (often two to three metres) are largely confined to poorly drained, flatter country. Duplex soils (those with two distinctly different origins) are commonly found in the channel banks and levees of major drainage lines. These soils have high pastoral productivity but are typically very susceptible to erosion. Soils across the VRD are generally low in phosphorus.

Sturt Plateau soils

On the gently sloping Sturt Plateau, soils are generally leached and deeply weathered. They are comprised of red and yellow earths and lateritic podzolic soils. Colluvial slopes are generally associated with duplex soils, and level non-lateritic plains with grey-coloured cracking clays.

Table 1: The relationship between parent material, soils and topography of the VRD
Parent Material
Soils and Topography

Basalt

  • red earths on sloping terrain
  • cracking clays* on lower to flat slopes
  • rock outcrop and/or very stony surfaces common

Limestone, dolomitic and calcareous sediments

  • earths and yellow earths on well drained slopes
  • cracking clays* on poorly drained, lower slopes

Sandstone and calcareous sandstone

  • sandy red earths
  • some yellow earths and lateritic podzolic soils

Non-calcareous shales (northern VRD)

  • yellow earths
  • soils also prevalent on floodplain deposits

Calcareous sedimentary rock or basalt

  • clays dominate alluvial plains

* The terms 'cracking clay' and 'black soil' are used interchangeably to describe the same soil. The technically correct term is vertisol.

 
You can view a map of geomorphic divisions in the Victoria River District on the Geology Page.
To make your own maps in the VRD, go to our Savanna Map Maker, link on this page.