Soil horizon A designation

A letter marking a mineral topsoil.

Also known as: Topsoil designation, Mineral surface horizon

Historical & archaeologicalScientificStandard profile

Meanings

The soil survey designation for a mineral surface horizon with accumulated organic matter.

Officially standardisedVerified fact
Designates a mineral surface horizon with accumulated organic matter.
Contexts: Technical drawing, Maps
Officially standardisedVerified fact
Is the layer most agriculture depends on, so its thickness recorded on a profile is among the most consequential single figures in a soil survey.
Contexts: Technical drawing, Maps

A capital letter written against a layer in a drawn soil profile, below the organic horizon where one is present.

IdentityHigh confidence: High confidence because the identity is documented in encyclopedic references.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is documented in encyclopedic references.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references.

Standard and guidance for archaeological field evaluation and excavation
Chartered Institute for Archaeologists · retrieved 2026-08-25
The professional standard for archaeological field recording in the United Kingdom, cited for recording conventions and the structure of a site archive. Practice differs between countries and between units, and records say where a convention is not universal.
Soil Survey Manual, horizon designation and texture classification
United States Department of Agriculture · retrieved 2026-08-25
The manual defining soil horizon letter designations and the texture triangle. Cited for what a designation means. Other national systems use different letters and records say where a convention is not universal.

Last reviewed 2026-08-25

Meanings

The soil survey designation for a mineral surface horizon with accumulated organic matter.

Officially standardisedVerified fact

Designates a mineral surface horizon with accumulated organic matter.

Officially standardisedVerified fact

Is the layer most agriculture depends on, so its thickness recorded on a profile is among the most consequential single figures in a soil survey.

Confidence

IdentityHigh confidence: High confidence because the identity is documented in encyclopedic references.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is documented in encyclopedic references.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references.

Sources

Standard and guidance for archaeological field evaluation and excavation
Chartered Institute for Archaeologists · retrieved 2026-08-25
The professional standard for archaeological field recording in the United Kingdom, cited for recording conventions and the structure of a site archive. Practice differs between countries and between units, and records say where a convention is not universal.
Soil Survey Manual, horizon designation and texture classification
United States Department of Agriculture · retrieved 2026-08-25
The manual defining soil horizon letter designations and the texture triangle. Cited for what a designation means. Other national systems use different letters and records say where a convention is not universal.

Last reviewed 2026-08-25