A horizons additional information
A1 horizon
Mineral horizon at or near the soil surface with some accumulation of humified organic matter. Usually darker than underlying horizon/s.
A2 horizon
Mineral horizon below the A1 horizon having, either alone or in combination, less organic matter, sesquioxides, or silicate clay than immediately adjacent horizons. Usually paler in colour than adjacent horizons.
Figure showing an example of A1 and A2 horizons
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Conspicuously bleached A2 horizon
80% or more of the horizon is bleached. Bleached horizons are very pale in colour. They are defined in terms of Munsell Soil Colour notation for dry soil. For all hues, it has a value 7 or greater and chroma 4 or less or where adjacent horizons have hues 5YR or redder, value 6 or greater with chroma 4 or less.
Ap horizon
A horizon/s where ploughing or other disturbance by humans has occurred. This includes disturbance by domestic animals and traffic that can lead to loss of natural structure, compaction and smearing of the soil. Severe compaction in Ap horizons can limit plant growth by restricting water entry and root proliferation.
Figure showing an example of Ap horizon
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Further information about soil compaction
Refer to the Field and Land Survey Handbook (Yellow Book) for further information on describing A horizons.