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Preparing the 3D view

Preparing lighting and the first complete frame…

Model scale

Illustrative 2 m profile. common geometric scale. no compulsory O–A–E–B–C sequence.

Temperate brown soil. Illustrative temperate profile; brown earth is not a USDA soil order.

How to read these results

Depths are teaching examples, not a field survey. E (eluviated) and R (hard bedrock) are valid designations but are absent from these exposed examples. Select a horizon label for its meaning.

Soil profile

Identify the horizons in a soil profile and compare how water, organic matter and parent material influence their development.

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Why it happens

A soil profile exposes horizons formed by organic inputs, weathering and material movement. Their colours and textures can provide clues, but not every soil contains every horizon.

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A measured field profile in Wuhlheide, Berlin. Colour and texture vary down the soil; horizon boundaries must be identified from field evidence.

Try a comparison

Compare the dark mineral surface in the Mollisol example. Switch to Oxisol and discuss gradual boundaries and intense weathering.

Reading the result

The selected profiles are examples; identifying a soil order also requires diagnostic properties beyond a colour match.

A common misunderstanding

Every soil contains the same sequence and thickness of horizons.

Soil profiles develop through interactions among parent material, climate, organisms, relief and time. Some horizons may be absent, weakly developed or altered by erosion and land use. Colour helps describe a profile, but classification also depends on diagnostic properties and processes.

Cases

Exam language

Horizon

A layer within a soil profile distinguished by properties such as colour, texture, organic matter or mineral accumulation. Horizons develop through soil-forming processes. Their boundaries can be gradual, and a real profile need not contain every named horizon.

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Layers in this exposed soil profile differ in colour and texture. These soil horizons record changes in organic matter, weathering and material movement.

O horizon

A soil layer dominated by organic material such as leaf litter and decomposing plant remains. It may overlie mineral horizons in some soils but be absent in others. Its thickness depends on inputs, decomposition and disturbance.

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White beech leaf litter at Carowiry Creek, New South Wales. Organic material on the forest floor stores carbon and provides material for decomposition.

A horizon

The mineral soil layer near the surface, where organic matter mixes with sand, silt and clay. Its darker colour often reflects humus, but colour alone does not establish fertility or the depth of the layer.

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Calciustoll near Ponce, Puerto Rico: a Mollisol with a roughly 30 cm mollic surface over a calcic horizon. Its parent material includes colluvium and weathered limestone.

E horizon

A soil horizon depleted in materials such as clay, iron or organic compounds that have been carried away by percolating water. It often appears paler than adjacent layers. Not every soil profile contains a distinct E horizon.

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Podzolic soil on the Karelian Isthmus. The pale E horizon has lost material by eluviation; material may accumulate in the B horizon below.

B horizon

A subsurface soil layer modified by soil-forming processes, often with an accumulation of clay or iron compounds moved from above. Compare its colour and structure with the A horizon; a B horizon is not simply any material beneath topsoil.

R horizon

Hard bedrock beneath a soil profile. It differs from loose or partly weathered parent material usually labelled the C horizon. Roots and water may still penetrate joints even where the rock remains consolidated.

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Rankosol over granite on Île de Berder, France. A shallow organic-rich surface over non-calcareous bedrock illustrates a ranker; horizons are real field layers, not a template.

Mollisol

A USDA soil order characterised by a dark, base-rich surface horizon, often formed beneath grassland. It is not an exact synonym for every chernozem classification.

Oxisol

A deeply weathered soil order common in humid tropical regions, typically rich in iron and aluminium oxides. Long weathering and leaching can leave a low supply of readily available nutrients. A red colour alone is insufficient for classification.

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USDA NRCS Nipe-series profile at Cerro Las Mesas, Puerto Rico, January 2002. Classified as Typic Acrudox, this Oxisol formed through deep weathering of iron-rich parent material.

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