##  [Soil Horizon](/soil-horizon-0) 

 Definition

A distinct, approximately horizontal layer within a soil profile with characteristic physical, chemical, and biological properties that differ from layers above and below.

 

 

 

 

 

 





## Principle

Principle

Soil horizons form by pedogenic processes—additions, losses, transfers, and transformations (e.g., organic matter accumulation, eluviation/illuviation, weathering, bioturbation)—that operate at or near the land surface over time to produce vertical differentiation.

 

 

 

 

 





## Demonstration

Demonstration

A surface organic-rich O horizon over a dark, humified A horizon, an eluviated pale E horizon beneath where clays and oxides were leached, and a B horizon where clays and iron have accumulated, together composing a typical diagnostic profile used for classification and management.

 

 

 

 

## Misapplication

Misapplication

Treating a single arbitrary excavation stratigraphic layer or a mechanically deposited fill as a pedogenic horizon without evidence of in situ soil-forming processes; or confusing horizon labels (e.g., 'A' vs 'B') across different classification systems.

 

 

 

 

 





## Consequence

Consequence

Correct identification of horizons informs land-use decisions, fertility management, drainage and engineering assessments, carbon accounting, and paleoenvironmental interpretation through vertical recording of soil-forming history.

 

 

 

 

## Reversal

Reversal

The reverse concept is an undifferentiated regolith or parent material lacking consistent vertical variation produced by pedogenesis—an absence of horizonation reflecting minimal soil development or recent deposition.

 

 

 

 

 





## Boundary

Boundary

Applies to layers formed by soil-forming processes in situ at or near the surface; excludes purely depositional strata of geological origin, construction fills, or transient litter layers that have not undergone pedogenesis.

 

 

 

 

 





## Semantic Tension

Semantic Tension

Tension exists between the morphological description of horizons (visual/texture/colour) and functional or classificatory definitions (process-based diagnostic criteria), which can shift how a layer is named or interpreted.

 

 

 

 

 





## Synthesis

Synthesis

A soil horizon is a vertically discrete unit within the soil profile produced by time-integrated pedogenic processes; combining morphological observation with process indicators allows consistent interpretation for management and science.