Level Up

Background

Classification is a basic requirement of all science and needs to be revised periodically as knowledge increases. It serves as a framework for organising our knowledge of Australian soils and provides a means of communication among scientists, and between scientists and those who use the land. The history of soil classification in Australia was reviewed by Isbell (1992), who noted that two classification schemes were widely used prior to 1996. The Handbook of Australian Soils (Stace et al. 1968) was largely a revision of the earlier great soil group scheme (Stephens 1953). The Factual Key (Northcote 1979) dates from 1960 and was essentially based on a set of about 500 profiles largely from south-eastern Australia. Moore et al. (1983) have discussed the advantages and disadvantages of these two schemes. The history of the development of the Australian Soil Classification is summarised in earlier editions and is presented in appendix 6. A number of options were considered before deciding on the current form.

Over the past five decades a vast amount of soils data has accumulated. Since the first edition was published considerable new information has been collected in wetland environments, and in the Northern Territory and Western Australia. This information needed to be incorporated into any new or revised national soil classification. The second edition mainly accommodates new knowledge about acid sulfate soils (sulfidic and sulfuric concepts), Subaqueous and Subtidal Hydrosols and introduces a new Sesqui-Nodular Suborder to the Tenosols. This third edition introduces a new soil order for deep sands, the Arenosols.

It is important to note that reference to the frequency or likelihood of occurrence of certain soil classes throughout the key in previous editions was based on the data available at the time of first edition publication.

The selected option for a new Australian classification system was for a multi-categoric scheme with classes defined on the basis of diagnostic attributes, horizons or materials (collectively called diagnostic features) and their arrangement in vertical sequence as seen in an exposed soil profile, that is, soil rather than geographic attributes were to be used.

Most diagnostic features are defined in the glossary, and all definitions, where applicable, are consistent with usage in the Australian Soil and Land Survey Field Handbook (NCST 2009). The Australian Soil and Land Survey Field Handbook is referred to in this publication as the Field Handbook (the Field Handbook is also colloquially known as the Yellow book due to the colour of its cover).

For clarity in this publication the levels in the classification are capitalised - e.g. Order, Suborder, Great Group, Subgroup and Family. This is not a requirement when using these terms outside of this publication

In the new scheme, classes are based on real soil bodies, they are mutually exclusive, and the allocation of 'new' or 'unknown' individuals to the classes is by means of a key.

The guiding principles are:

  1. The classification should be a general purpose one as distinct from a technical or special purpose scheme.
  2. It should be based on Australian soil data and as far as possible the selected attributes should have significance to land use and soil management.
  3. It should be based on defined diagnostic features, the definitions of which, where appropriate, should be compatible with those of major international classification schemes.
  4. The entity to be classified is the soil profile, with no depth restrictions in definition except for the 1.0 m depth criterion for the Arenosol order.
  5. Although the soil classification should be based as far as practicable on field morphological data, laboratory data must be used as appropriate. If possible, more use should be made of soil physical and engineering properties.
  6. The scheme should be based on what is actually there rather than on what may have been present before disturbance by humans. Surface horizons should not be defined in terms of an 'after mixing' criterion as in Soil Taxonomy (2014).
  7. The scheme should be a multi-categoric one, arranged in different levels of generalisation.
  8. The scheme should be flexible enough to accept new knowledge as it becomes available - it should be open-ended.
  9. The classification should give emphasis to relatively stable attributes as differentiae.
  10. The nomenclature must not be too complex, but be unambiguous.

Applying principles b) and c) appropriately and consistently may prove difficult for some soils. In particular where diagnostic features are only observed at significant depth, judgement is required as to which principle should have precedence. Guidance to assist with this is provided in the key.

The guidelines above have been followed in the new scheme. Unfortunately, because of lack of data, it has not been possible to make more use of soil physical and engineering properties.