SOIL222 - Topic 7: Soil Classification

Identify and understand the various soil classification schemes used in Australia

• Australian Soil Classification (ASC): This is the current national system for classifying soils in Australia. It establishes 15 soil orders based on diagnostic horizons and attributes relevant to local conditions, reflecting the unique characteristics of Australian soils.

• Unique Characteristics of Australian Soils: Australian soils often do not fit well into international systems due to old landforms and polygenetic soils.

• Soil Classification Systems in Australia (Historical Context):

  • Great Soil Groups: Over 40 groups that emphasized climate-vegetation-soil relationships.

  • Factual Key (Northcote, 1979): Based on field-observed features without making assumptions about soil genesis.

• General Soil Classification: Soils are classified based on diagnostic horizons, soil color, structure, organic matter content, chemistry, pH, exchangeable sodium percentage, and clay content.

• International Systems (for context):

  • Soil Taxonomy: Developed by USDA, a complex system based on diagnostic horizons and properties, structured into orders, suborders, groups, etc.

  • World Reference Base (WRB): An international standard for soil classification that accommodates diverse soil forms.

Describe and apply the concept of land capability

• Concept of Land Capability:

  • Definition: The inherent capacity of land to sustain a particular land use over a long period without permanent damage to the land or its resources.

  • Purpose: To guide sustainable land management decisions by assessing the physical potential and limitations of land units for various uses (e.g., cropping, grazing, forestry, conservation).

  • Application: Involves evaluating a range of biophysical factors, including soil type, slope, climate, geology, hydrology, and erosion risk, to determine the most appropriate and sustainable land uses that prevent land degradation and maintain productivity.

Briefly describe the eight Rural Land Capability classes of Emery (1986) and the more recent Land and Soil Capability Classification, and use these to classify land

• Rural Land Capability Classes (Emery, 1986):

  • A system developed primarily for New South Wales, classifying land based on its limitations for agricultural production.

  • Eight Classes (I-VIII): Progress from minimal limitations (Class I) to very severe limitations (Class VIII):

    • Class I: Very high capability land; suitable for intensive cultivation with minimal limitations.

    • Class II: High capability land; suitable for regular cultivation with minor limitations, requiring simple management practices.

    • Class III: Moderate capability land; suitable for restricted cultivation, requiring careful crop rotation and conservation practices.

    • Class IV: Low capability land; marginal for cultivation, suitable for occasional cropping with intensive conservation, or frequent pasture improvement.

    • Class V: Very low capability land; unsuitable for cultivation but suitable for pasture improvement or forestry; requires careful management.

    • Class VI: Grazing land; unsuitable for cultivation, limited by severe physical constraints; suitable for grazing or forestry with extensive conservation.

    • Class VII: Forest or wilderness land; very severe limitations, unsuitable for grazing or cultivation; suitable for extensive forestry, nature conservation, or wilderness.

    • Class VIII: Extremely low capability land; highest limitations, suitable only for wilderness or protection purposes.

• Land and Soil Capability (LSC) Classification (More Recent):

  • A more recent and comprehensive classification system adopted in many Australian states (e.g., NSW LSC version 2.0).

  • Builds upon previous systems but incorporates a wider range of biophysical factors and considers the impact of specific land uses on soil and water resources.

  • Key Objectives: To provide a clearer, more consistent framework for assessing land's suitability for sustainable land use, taking into account inherent natural land qualities and the dynamic impacts of land management.

  • Classification Process: Involves assessing a combination of specific land attributes and hazards (e.g., soil erosion hazard, soil structural decline hazard, soil acidification hazard, salinity hazard, waterlogging hazard, shallow soil/rock outcrop) to derive an overall capability class. The classification guides land-use planning by categorizing land into specific classes that indicate the range of sustainable uses and risk levels for degradation based on land characteristics and management requirements.