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Soil Evaluation of Biological Productivity

Why is Soil Biology Important? | What Regulates Soil Biology? | Measuring Soil Biology | Management and Soil Biology

Why evaluate soil?

Soil is the key resource for building and subsequently evaluating sustainable land management systems.
Its effective utilisation very much depends on understanding how it is put together, and why things happen within it.

Soil varies in space and time. Its productivity is highly dependent on inherent qualities, weather, and management. Relatively simple observation and analysis give clues to both strengths and weaknesses. Such knowledge is invaluable in preparing and evaluating management options.

The productive vigour of soil for a given set of climatic circumstances depends on the following characteristics. Each characteristic can be broadly assessed in the field. Questions to assist assessment are listed under each characteristic

Air and water movement into the soil

  • What is the surface condition?
  • Does water sit on the soil surface?
  • Is mineral soil exposed?
  • Is it hard set or crusted?
  • Does it break into aggregates when gently disturbed?
  • Is the surface structure robust?
  • Is there evidence of separation of soil grains at the surface?
  • Is there adequate soil surface protection by organic material?
    Quantity of pores within the soil
    • Is more than half the soil volume actual pore space?
    • Is there a good distribution of pores of a range of sizes?
    • Are there ‘free draining’ pores?
    • Are there plenty of ‘capillary pores’ to supply moisture to plant roots?
    • Are the pores resilient over time?
      Organic activity in the topsoil layers
      • Does organic matter accumulate on the soil surface?
      • Is there much earthworm, insect, and spider activity helping to incorporate the surface organic matter?
      • Is there other biological activity in the top portion of the soil?
      • What is the density of plant roots and where are they?
      • Is there an accumulation of humus and other organic debris within the soil?
        Conductivity through the soil
        • Are the pores interconnected?
        • Can the free draining pores successfully transmit their water? ie does waterlogging occur?
        • Can air move into and through the profile to allow plant and animal respiration?
        • Are there layers in the profile which can specifically impede movement of either air or water?
          Nutrient status
          • Are there adequate nutrients available for plant roots to collect?
          • Is the pH affecting this?
          • Are there any toxic materials about (including sodium chloride)?
            Depth of the soil
            • Is the soil material present in sufficient quantities to foster a vigorous and dynamic biological community?
            • What are the plant roots doing?
              Evaluating soil for engineering uses

              When used for engineering purposes (roads, dams or buildings) the requirements are quite different to those for maximising biological activity. These are discussed at the soil evaluation for engineering purposes page.


              How then to appraise a soil in light of these questions?

              The range of analysis tools in a "tool-box" (apart from eyes, hands and ears) can include:
              1. Field tools (shovel, auger, palette knife, fresh water bottle)
              2. Hand lens
              3. Hand texturing technique
              4. Dispersion test method
              5. Colour charts
              6. pH kit
              7. Careful observation

              Further information
              The Australian Governments “Soil Health Knowledge Bank” provides useful information on soil analysis and testing.

              A summary of tools currently used to assess soil health at the farm or paddock scale is given in the report Tools and systems for assessing soil health.

              Related Links

              Further information about Soil Biology.
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