What are A-horizon and O-horizon?


• O horizons are soil layers with a high percentage of organic matter.
• The O horizon is the upper layer of the topsoil which is mainly composed of organic materials such as dried leaves, grasses, small rocks, twigs, surface organisms, fallen trees, and other decomposed organic matter.
• It contains about 20 to 30% of organic matter.
• Typically within a woodland area there are three distinct organic layers:
1. one of leaves pine needles and twigs (Oi)
2. underlain by a partially decomposed layer (Oe)
3. a very dark layer of well decomposed humus (Oa).

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Updated on: 10-Oct-2022

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