Agriculture Reference
In-Depth Information
Improved Communication Through Use of Soil Profile Class and Soil Group
Taxonomic Classifications
A Soil ProÝle Class is a group, or class, of soil proÝles, not necessarily contiguous, which may
be grouped on the similarity of their morphological characteristics and possibly some laboratory-
determined properties. In Australia, the Soil ProÝle Class is deÝned at various levels of generali-
zation (e.g., series, family, great soil group or phase, depending on the information available and
the purpose of the survey and map scale (Gunn et al., 1988; Chapman and Atkinson, 2000). Soil
classes and mapping units are not identical. Butler (1980) discusses the distinction between soil
classiÝcation units and soil mapping units:
The search for a merging between soil taxonomic entities (soil classes) with landscape area units
(mapping units) has not been very successfulÐeither we adopt a soil classiÝcation from the landscape
itself in which case it Ýts in the landscape but not the rest of a soil taxonomic system designed to
cover a wider area, or we impose the classes of a general taxonomic system on the landscape, and
then it is unlikely to Ýt local soil modes or the individual character of the local landscape scene.
Butler (1980) supports the concept to Ñdevelop and use the soil classiÝcation that arises
from the landscape itself,Ò and contrasts this approach with national classiÝcations, which may
in some instances coincide with soil classes, but may even cross boundaries in the national
scheme (Butler, 1980; McKenzie and Austin, 1989). Soil classes are usually based to some
extent on a national classiÝcation scheme (e.g., deÝning them by incorporating their local
uniqueness but also recognizing afÝliations with a national scheme). For example, this has
been done in various ways in each state by combining a local name with the taxonomic name,
e.g., Dorrigo Red Ferrosols.
In several states and regions in Australia, a soil classiÝcation system or key has been devised
especially to assist with the communication of soils information at a general level and to be suitable
for use at the mapping scales required (i.e., regional). Each classiÝcation system has taken into
account the most important features of that state or region. For example, in the western region of
New South Wales, the devised soil classiÝcation system (Murphy and Murphy, 2000) uses soil
physical properties (inferred from soil texture) as an indicator of inÝltration rate and water-holding
capacity, presence of root-restricting layers, along with micro-topography (e.g., Gilgai) (Table 9.1).
Use is also made of ÑSpecial Soil GroupsÒ (Murphy et al., 2000; Table 9.1) as a basis for problem-
oriented investigations, because the existing general-purpose soil classiÝcation systems do not
adequately describe or account for them. In South Australia, Soil Groups and Soil Classes were
developed using the presence of calcium carbonate (e.g., calcareous soils or depth to calcrete) at
the highest level of classiÝcation, because calcareousness is a major component of South Australian
soils, and has particular impact on speciÝc needs for assessment and management work (Wetherby
and Oades, 1975; Table 9.2). In contrast, many readily recognized soils with related management
implications in Western Australia are distinguished by the relative abundance of ironstone gravels
present (Figure 9.2).
Soil Groups and Classes of South Australia
Despite the trend toward mapping and land description based on speciÝc soil and landscape
attributes, there remains a need for a form of soil classiÝcation, which distinguishes key soils at
the regional level. This is considered necessary for communication, and indeed for some GIS-based
modeling applications. The Great Soil Groups described by Stace et al. (1968), although still widely
used locally for convenience, are inadequate due partly to loose deÝnitions, but mainly to the reality
that many South Australian soils simply do not Ýt into any of the Groups. The Australian Soil
ClassiÝcation (Isbell, 1996) was extremely useful in the development of a labeling system for soil
