Syllabus Edition
First teaching 2015
Last exams 2025
Soil Profiles
Written by: Alistair Marjot
Reviewed by: Bridgette Barrett
Soil Profiles
Soil profiles provide a visual representation of the different layers or horizons present in a soil system
These horizons reflect the processes and materials that have shaped the soil over time
There are six main horizons
A soil profile is a visual representation of the different horizons present in a soil system
O horizon
The O horizon, also known as the organic horizon, is the uppermost layer
It is composed mainly of organic matter such as leaf litter, decaying plant material, and organic debris
It is rich in nutrients and serves as a site for nutrient cycling and organic material decomposition
A horizon
The A horizon, also called the topsoil, 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 and provides a favourable environment for root development
E horizon
The E horizon, also known as the eluvial or leached horizon, 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, 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 typically 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, 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
These layered horizons in a soil profile provide information about the soil's composition, nutrient content, water-holding capacity, and drainage characteristics
They help scientists, farmers, and land managers understand the properties and fertility of soils, enabling them to make informed decisions regarding land use, crop selection, and soil conservation practices
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