Soil Profiles (DP IB Environmental Systems & Societies (ESS))

Soil Profiles

• Soils develop a stable, layered structure known as a profile

  • Soil profiles are made up of different horizons (layers)

  • Over a long period of time, interactions and processes within the soil system produce these horizons

• Soil profile diagrams provide a visual representation of the horizons present in a soil system

  • There are six main horizons

O horizon

• The uppermost layer is the O horizon, also known as the organic horizon

• It is composed mainly of organic matter such as leaf litter, decaying plant material and organic debris

• It is rich in nutrients

• It serves as a site for nutrient cycling and organic material decomposition

A horizon

• The A horizon, also called the topsoil

• It is a mixed mineral and organic horizon

• It is usually darker in colour due to the accumulation of organic matter

• This layer is important for plant growth as it contains nutrients

• It provides a favourable environment for root development

E horizon

• The E horizon, also known as the eluvial or leached horizon

• It is characterised by the leaching or removal of minerals and nutrients due to downward movement of water

• It often appears lighter in colour than the surrounding horizons

B horizon

• The B horizon, also called the illuvial or deposited horizon

• It is the layer where minerals and nutrients leached from the upper horizons accumulate

• It often exhibits different colours, textures, or chemical properties compared to the horizons above and below it

C horizon

• The C horizon represents the weathered parent material from which the soil has formed

• It is composed of partially weathered rock fragments and may contain limited organic matter

• The properties of the C horizon influence the development and characteristics of the upper horizons

R horizon

• The R horizon, also known as bedrock

• It is the underlying solid rock that forms the base of the soil profile

• It is often unweathered

• It is relatively unaffected by biological activity and represents the original geological material from which the soil formed

• The distinctive horizons in a soil profile show a transition from more organic components in the upper surface to more inorganic components in the layers below

• These layered horizons provide information about the soil's

  • Composition

  • Nutrient content

  • Water-holding capacity

  • Drainage characteristics

• They help scientists, farmers, and land managers understand the properties and fertility of soils

  • This helps them to make informed decisions regarding land use, crop selection and soil conservation practices