Do you know there are different types of soil horizons? Remember, soil horizons are the layers of soil. They are parallel to the surface of soil. However, it’s the major traits found in each that defines the different types of soil horizons listed by the US Department of Agriculture (USDA).


Unlike horizons, soil layers are when all soil properties are thought to be caused by its parent material.

O Horizons or Layers

These are layers dominated by organic material. There are two kinds of O horizons or layers. The first one is soil that were or are saturated with water for lengthy periods of time. If the soil was once soaked with water, it was later drained. The second kind has never been saturated in water.

A Horizons

A horizons form at the surface or beneath O horizons or layers. However, the materials have changed. They may have a mixture of humified organic matter mixed with mineral fractions. Or, human activity changed their properties. However, they cannot have characteristics dominated by E or B horizons.

E Horizons

Then, there are E horizons. They have a concentration of sand and silt particles. A loss of silicate clay, iron, or aluminum causes this. In some cases, it’s a combination of those three.

B Horizons

B horizons form below an A, E, or O horizon. Also, they contain soil structure (the combination of sand, silt, and clay particles assembled). In addition, they contain silicate clay, iron, aluminum, humus, carbonates, gypsum, or silica spread across layers. They can also show signs that carbonates were removed. Sometimes, there is leftover sesquioxides that’s concentrated. Other times it’s in coatings. Or, if there are moisture changes, additional alterations appear. Finally, it has brittleness.

C Horizons or Layers

C horizons or layers lack properties of any of the horizons listed above. Also, they aren’t very affected by soil formation processes. C horizons or layers don’t include hard bedrock.

R Layers

Finally, R layers are made up of hard bedrock.

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