Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
Definition
A horizon is a distinct layer of soil that has unique physical and chemical properties compared to other layers. These horizons are part of the soil profile and influence plant nutrition and soil health.
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Horizons are identified by letters such as O, A, B, C, and R, each representing different characteristics.
The A horizon, also known as topsoil, is rich in organic material and crucial for plant growth.
B horizon or subsoil contains minerals leached from the A horizon but has less organic matter.
The C horizon consists of weathered parent material from which the upper layers derive.
Soil horizons form through processes like leaching, organic matter accumulation, and weathering.
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Related terms
Soil Profile: A vertical section of soil that shows all its horizons.
Leaching: The process by which soluble substances are washed out of the soil into lower layers.
Organic Matter: Decayed plant and animal residues in the soil which contribute to fertility.