201SOILS

SOILS

This is a series of 3 lectures covering the following aspects of soils and working with them in the environment.

Susan White, April 1998

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What is Soil?

Definitions of soil.
Regolith
Weathering and soil

Physical Properties of Soils

Soil Profiles
Horizons
Descriptions
- colour,
- texture,
- structure
Soil constituents

Soil Formation

5 soil forming factors
Processes of soil formation
- leaching and eluviation,
- precipitation and illuviation,
- sesquioxides and soil colour.

How soils form and change with time

Soils and landforms

Catenas,
Soil Associations.

Soil classification

Great Soil Groups
Climatic
- Zonal,
- Intrazonal,
- Azonal.
US -7th Approximation;
- this system has many new soil names and is used in countries receiving US aid.
FAO/Unesco Soil map of the world
- internationally agreed for map of the world; a mixture of Great Soil Group names and terms similar to the US system.
Australia
- Northcote - nongenetic system and
- Isbell - 1990s; the most recent of several CSIRO systems.
Working with soils in the environment
- Soil maps and reports
  - Australia
    - Atlas of Australian Resources series.
    - Northcote Soils Atlas of Australia.
  - Victoria
    - Victorian Year Book 1964: this put together the 3 sheets by Northcote covering Victoria and altered the key.
    - Atlas of Victoria: the map of land types is essentially a soils map.
    - Department of Agriculture and Soil Conservation Authority reports and maps.
      The summary on the reverse of the soil map of Australia in the Atlas of Australian Resources (2nd ed. 1963) covers soil maps to that date, including early soil maps of CSIR and CSIRO for the irrigation areas, university research projects eg Gellibrand and Berwick, Soil Conservation Authority and Dept. of Agriculture maps.
Personal research - work it out for yourself !
- Use a geological map (parent material approach), a topographic map, and air photos.
  - Take note of the topography (toposequence approach).
  - Take note of the vegetation and land use.
  - Consider the climate.
- Sampling
  - field sampling using description by
    - Horizons and sub horizons,
    - depth,
    - topographic position,
    - slope and aspect,
    - land use etc.
    - Grid sampling vs land systems approach.
- Analysing soils - field or laboratory
- Mapping soils - mapping units and full descriptions.
Summary
- Soils overlie and may indicate the rock or regolith below.
- Soils may have formed on the rock or regolith underlying them, or may be in part completely formed on added material deposited by wind, water, mass movement, ice.
- Soils record the passing of time - perhaps thousands of years of weathering on a stable surface, or a more complicated sequence of erosion and deposition and weathering, in some combination.
- Soils reflect changing climate, vegetation and organic activity both past and present.
- Australian soils are often old, deeply leached, poor in organic matter and susceptible to erosion if conditions change

References
Ollier, CD, 1969 (and later editions) Weathering
Corbett, JR, 1969 The Living Soil
Leeper, GW and Uren, N, 1993 Soil Science: An Introduction
Stace et al., 1968 A Handbook of Australian Soils
Chapman, PEV & Murphy, BW, 1991 Soils - their properties and management.
McTainsh, G. & Broughton, W. (eds) Land degradation processes in Australia.
Division of Soils, CSIRO, 1983 Soils: An Australian Viewpoint.

and to encourage you to search the WWW for more advice, try here!

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SOME SOIL DEFINITIONS

Podzol (Russian = ashy)	Grey surface, acid throughout, bleached subsurface (A₂), often organic layer on top (A₀). The Australian podzol has sharply contrasting clay B horizon and no organic layer.
Chernozem (Russian = black land)	Black, Ca-saturated, stable well-marked aggregates, 5 mm in surface, coarser in subsoil, calcareous subsoil, no contrast in texture. In Australia, Black earth is used for a grey soil with organic content below 4%.
Krasnozem, red loam	Red-brown highly aggregated crumbs on surface, no contrast in profile, less organic content with depth, very well aggregated and permeable red subsoil; resistant to erosion; acid throughout.
Red-brown earth	(Aust.) - red-brown loamy A, red clay B₁and commonly calcareous clay B₂; acid on top, alkaline below.
Terra Rossa	(red soil of the Mediterranean area) red soil, usually of heavy texture due to high clay content, and shallow in depth, overlying parent limestone rock with a sharp junction, which is often irregular, with soil pipes. Rendzina, Groundwater Rendzina and Terra Fusca are other limestone soils.
Laterite	(a) a whole deep profile with kaolin and ferric oxide dominant; (b) massive ironstone as a relict of an older soil; (c) in America, a red soil.
Desert	Pink and pale red soils, light-textured, humus lacking, salts leached up to surface, giving efflorescences and crusts of halite, gypsum, carbonate, iron oxide, silica, or pans within soil, often exposed by later wind deflation.
Mallee	(Aust.) - brown solonised sandy or loamy alkaline A, more clayey, alkaline, calcareous and saline B.
Grey and brown soils of heavy texture	(Aust.) - nutty or crumb structured, slightly sandier A horizon, neutral, over cloddy B horizon with small amounts of lime or gypsum, and dull-coloured mottling (better developed in grey soil on less well-drained areas); crab-holes or gilgai (Aust.), hummocky surface related to swelling and cracking.

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