3.4 The soil system

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3.4.1: Outline how soil systems integrate aspects of living systems.

Soils are major components of the world's ecosystems. They form at the interface of the Earth's atmosphere, lithosphere (rocks), biosphere(living matter) and hydrosphere (water). Soils form the outermost layer of the Earth's surface, and comprise weathered bedrock(regolith), organic matter (both dead and alive), air and water.

Soil has matter in all three states:
  • organic and inorganic matter form the solid state
  • soil water(from precipitation, groundwater and seepage) form the liquid state
  • soil atmosphere forms the gaseous state

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The Soil interact with the atmosphere, lithosphere, biosphere and hydrosphere.
  • The water cycle moves through the soil by infiltration and water may evaporate from the surface
  • The atmosphere may contain particulate matter that is deposited on the soils and praticles may blow up into the atmosphere
  • Rocks in the lithosphere weather to form soils, and soils at depth and pressure may form rocks
  • Plants in the biosphere may extract nutrients from the soils and dead plants may end up forming parts of the soil

Soil profile/ Soil horizon
File:Soil profile.png
File:Soil profile.png

  • O) Organic matter: Litter layer of plant residues in relatively undecomposed form.
  • A) Surface Soil: Layer of mineral soil with most organic matter accumulation and soil life. This layer eluviates (is depleted of) iron, clay and calcium, organic compounds, and other soluble constituents. When eluviation s pronounced, a lighter colored "E" subsurface soil horizon is apparent at the base of the "A" horizon. A-horizons may also be the result of a combination of soil bioturbation and surface processes that winnow fine particles from biologically mounded topsoil. In this case, the A-horizon is regarded as a "biomantle".
  • B) Subsoil: This layer accumulates iron, clay, aluminum and organic compounds, a process referred to as illuviation.
  • C) Parent Rock: Layer of large unbroken rocks. This layer may accumulate the more soluble compounds

Transfers of materials (including deposition) results in reorganization of the soil. There are inputs of organic and parent material precipitation, infiltration and energy-outputs include leaching, uptake by plants and mass movement. Transformations include decomposition, weathering and nutrient cycling.

3.4.2: Compare and contrast the structure and properties of sand, clay and loam soils, including their effect on primary productivity.

Water retention and availability
Nutrient storage capacity
Air Space
Primary Production
Sticky and easily waterlogged
Fast draining soils that dry outs easily
High to Medium

Primary productivity of soil depends on:
  • mineral content
  • drainage
  • water-holding capacity
  • airspaces
  • biota
  • potential to hold organic materials

Soil Triangle from the US Dept of Agriculture
Soil Triangle from the US Dept of Agriculture

http://sciencebitz.com/?page_id=189 (More info)

3.4.3: Outline the processes and consequences of soil degradation
Soil degradation: the decline in quantity and quality of soil. It is also erosion by wind and water, biological degradation (loss of humus and plant or animal life), physical degradation (loss of structure, changes in permeability), chemical degradation (acidification, declining fertility, changes in pH, salinity).

Grazing by livestock at high density remove vegetation cover
Increase in soil erosions by wind and water and can lead to desertification
Removal of forest cover
Increase in Soil erosion
Unsustainable agriculture
Remove upper soil horizons
Use of chemicals could damage the soil
Can lead to soil stalinization
Stress for plants and can damage agricultural productivity
Wind and water can remove upper layers of the soil, removing organic material, minerals and nutrients
Impact on water quality-can cause floodImpact on air quality- dust
Enlargement of deserts
Can cause crop failure and lead to malnutrition and famine


http://www.acsgarden.com/articles/other-gardening/soil-degradation.aspx (More info)

3.4.4: Outline soil conservation measures

Soil Conservation
Reduce surface run-off and erosion
Wind breaks
Lines of trees to prevent wind erosion
Lime is added to the soil to reduce acidity
Trickle drip
Slow release of water from pipes under the surfaces can reduce the loss of evaporation
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http://yesitsyomoma.wordpress.com/2011/03/30/revision-topic-3-4-the-soil-system/ (More info)