A Horizon Definition

āhərīzən
noun
In ABC soil, the uppermost, darkest zone that is rich in organic matter.
American Heritage
The uppermost soil zone, containing humus.
Webster's New World
Synonyms:
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other
In ABC soil, the uppermost, darkest zone that is rich in organic matter. The upper section of the A horizon usually contains humus along with plant and animal matter in varying stages of decay. The middle section usually contains a high concentration of quartz or other minerals that remain following the leaching away of clay, iron, and aluminum. The lower section is typically transitional in nature between the A horizon and the B horizon.
American Heritage Science
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