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Definition of "A" horizon

Categorized under "General"

Definition as written by spklatt:

The surface layer of a soil; also called topsoil. This is the soil layer having maximum organic matter accumulation, maximum biological activity and/or eluviation (leaching out) of materials such as iron and aluminum oxides and silicate clays.

The A horizon can be anywhere from 0 to 40 cm thick, or more. Grasslands tend to have the thickest A horizons, because much of the organic matter in the soil is added by their deep, fibrous root systems underground, as opposed to organic matter that mostly rests on the surface, like on a forest floor.

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