Conversion of the Atlas of Australian Soils to the Australian Soil Classification

Abstract

This dataset was supplied to the Bioregional Assessment Programme by a third party and is presented here as originally supplied. Metadata was not provided and has been compiled by the Bioregional Assessment Programme based on the known details at the time of acquisition. The following abstract is taken from the report supplied with the original dataset.

The Atlas of Australian Soils (Northcote et. al. 1968) was produced between 1960 and 1968. There are 3060 unique mapping units, describing 22 560 polygons, which are defined on the basis of soil, landform, parent material and vegetation. Within each unit, dominant and subdominant soil types have been presented, using the Northcote Principal Profile Form (PPF). Some units have as many as 28 PPF's recorded. McKenzie and Hook (1992) used the descriptions to identify a dominant PPF for each of the Atlas mapping units. This has enabled interpretative information (eg. soil texture) to be linked to the Atlas to produce broad scale spatial estimates across Australia. A provisional correlation table between Atlas Mapping Units and Soil Orders in the Australian Soil Classification has been prepared recently.

The ASC Look Up Table (LUT) was developed in conjunction with Concepts and Rationale of the Australian Soil Classification (Isbell et al 1996). The purpose of the table was to enable plots of the distributions of the ASC orders to be created with an estimate of the area of each order, and used to enhance descriptions of the "General Occurrence and Environment" of each Order.

Dataset History

Metadata was not provided and has been compiled by the Bioregional Assessment Programme based on the known details at the time of acquisition. The following history is taken from the report supplied with the original dataset.

Method

In 1994, Graham Murtha and Warwick McDonald (CSIRO Division of Soils) began the development of a translation of the Principal Profile Forms (PPF) listed as dominant in the Atlas, to the new Australian Soil Classification (ASC). The translation and subsequent LUT attempted to identify the ASC, down to the suborder level, with an estimate of the accuracy based on the number of PPF's listed for each map unit. This table formed the basis for the Isbell et al (1996) ASC table, which has developed further, to rely more on the full descriptions and personal experience within some areas.

Ray Isbell used plots created from the Murtha/McDonald table, at a scale of 1:23 000 000, to locate areas where, from his personal experience, there was some doubt in the translation. Using the original Atlas maps (1:2 000 000), Isbell identified the mapping units in question and referred back to the full unit descriptions. In some cases, the PPF designated as dominant did not appear appropriate, was not defined clearly enough or was too ambiguous to make a translation (eg. Red Duplex soils (Dr) span several orders). Previous experience and the unit descriptions allowed an acceptable estimate to be made. Many iterations of this process were carried out during 1995/96, before final distribution plots were accepted and used as an aid to describing the occurrence of the new soil classification orders (Isbell et al 1996).

Limitations

Knowledge of the methods used to create the Atlas of Australian Soils is necessary to appreciate limitations of the new coverage predicting the dominant ASC Order. The accuracy of the conversion of the dominant PPF's in the Atlas to the ASC is further constrained by the following.

* The accuracy of the conversion varies spatially and depends on the quality of published information in each region and personal experience of contributing authors (primarily Ray Isbell).

* Plots at a scale of 1:23 million were used to verify the accuracy of the table. Application of the ASC LUT at larger scales will not be reliable.

* The table is based on the assumption that each PPF thought to be dominant in an Atlas polygon can be readily equated with a particular ASC order. This is a false premise in a number of instances and other assumptions have to be made - for example, sodicity (ESP) is not used in the Factual Key (and hence not in the Atlas) so the identification of Sodosols has to be based on morphological criteria - in this case a useful guide is the presence of a strongly bleached A2 horizon overlying a clay subsoil B horizon.

* PPF's listed for each of the mapping units in the ASC LUT do not necessarily agree with those previously identified as being dominant (eg. in McKenzie & Hook 1991)

* The quality of the original Atlas mapping varies substantially and an indication of reliability is provided with the original explanatory notes published during the 1960's: it should be heeded.

* The dominant soil for each map unit may occupy a very limited area (perhaps 20%) within that unit. Any analysis based on an interpretation of the dominant soil is therefore of restricted value.

* It is normal for there to be a very large variation within each map unit. Some units have up to 20 soils listed. It is common for the within unit variation to be as great as the between unit variation - this is an inescapable problem with reconnaissance scale soil mapping.

Dataset Citation

CSIRO (2001) Conversion of the Atlas of Australian Soils to the Australian Soil Classification. Bioregional Assessment Source Dataset. Viewed 29 September 2017, http://data.bioregionalassessments.gov.au/dataset/295707d5-2774-4ca5-a539-6c0426bbd662.