A Horizon (Topsoil)
The A horizon is usually the surface horizon. This is an area of high biological activity with the greatest organic matter content. It is also a zone of leaching. As precipitation enters the A horizon, it dissolves soluble soil organic compounds and minerals. These dissolved compounds are then moved downward through the soil profile. Most plant roots are found in the A horizon.
B Horizon (Subsoil)
The B horizon lies underneath the A horizon. This layer usually contains less organic matter than the surface layer but accumulates the dissolved materials leached from the A horizon(clays, iron oxides, aluminum, and dissolved organic compounds). For this reason, the B horizon typically contains more clay than the surface layer. The accumulated products in the B horizon increase over time as the soil forms.
C Horizon
The C horizon contains unconsolidated material that has been minimally affected by the soil forming factors. It lies beneath the B horizon, and may or may not be the same as the parent material from which the soil formed.
AGBB 2090 Soil Horizons
Melissa Kreider
Created on November 19, 2024
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Transcript
A Horizon (Topsoil)
The A horizon is usually the surface horizon. This is an area of high biological activity with the greatest organic matter content. It is also a zone of leaching. As precipitation enters the A horizon, it dissolves soluble soil organic compounds and minerals. These dissolved compounds are then moved downward through the soil profile. Most plant roots are found in the A horizon.
B Horizon (Subsoil)
The B horizon lies underneath the A horizon. This layer usually contains less organic matter than the surface layer but accumulates the dissolved materials leached from the A horizon(clays, iron oxides, aluminum, and dissolved organic compounds). For this reason, the B horizon typically contains more clay than the surface layer. The accumulated products in the B horizon increase over time as the soil forms.
C Horizon
The C horizon contains unconsolidated material that has been minimally affected by the soil forming factors. It lies beneath the B horizon, and may or may not be the same as the parent material from which the soil formed.