5.1 Introduction to soil systems

Significant ideas:

  • The soil system is a dynamic ecosystem that has inputs, outputs, storages and flows.
  • The quality of soil influences the primary productivity of an area.

Knowledge and understanding:

  1. The soil system may be illustrated by a soil profile that has a layered structure (horizons).
  2. Soil system storages include organic matter, organisms, nutrients, minerals, air and water.
  3. Transfers of material within the soil, including biological mixing and leaching (minerals dissolved in water moving through soil), contribute to the organization of the soil.
  4. There are inputs of organic material including leaf litter and inorganic matter from parent material, precipitation and energy. Outputs include uptake by plants and soil erosion.
  5. Transformations include decomposition, weathering and nutrient cycling.
  6. The structure and properties of sand, clay and loam soils differ in many ways, including mineral and nutrient content, drainage, water-holding capacity, air spaces, biota and potential to hold organic matter. Each of these variables is linked to the ability of the soil to promote primary productivity.
  7. A soil texture triangle illustrates the differences in composition of soils.

Applications and skills:

  • Outline the transfers, transformations, inputs, outputs, flows and storages within soil systems.
  • Explain how soil can be viewed as an ecosystem.
  • Compare and contrast the structure and properties of sand, clay and loam soils, with reference to a soil texture diagram, including their effect on primary productivity.


  • Significant differences exist in arable (potential to promote primary productivity) soil availability around the world. These differences have socio-political, economic and ecological influences.

Theory of knowledge:

  • The soil system may be represented by a soil profile—since a model is, strictly speaking, not real, how can it lead to knowledge?


  • Communities and ecosystems (2.2)
  • Flows of energy and matter (2.3)
  • Investigating ecosystems (2.5)
  • Biomes, zonation and succession (2.4)
  • Introduction to water systems (4.1)
  • Terrestrial food production systems and food choices (5.2)
  • Soil degradation and conservation (5.3)
  • Acid deposition (6.4)
  • Climate change (7.1 and 7.2)
  • Resource use in society (8.2)
  • Solid domestic waste (8.3)