A soil profile is a vertical section of the soil that displays all of its horizons. It extends from the soil surface to the parent rock material. Horizons are distinct layers within a soil profile, each with its own set of characteristics. The major horizons commonly found in soil profiles are the O horizon, A horizon, E horizon, B horizon, C horizon, and R horizon.
Key Facts
- Soil Profile: A soil profile is a vertical section of the soil that depicts all of its horizons. It extends from the soil surface to the parent rock material.
- Horizons: Horizons are distinct layers within a soil profile, each with its own set of characteristics. The major horizons commonly found in soil profiles are:
a. O Horizon (Organic): This horizon consists mostly of organic matter, such as decomposing leaves. Its thickness varies in different soils and may be absent in some cases.
b. A Horizon (Topsoil): The A horizon is primarily composed of minerals from the parent material, along with incorporated organic matter. It is a fertile layer that supports plant growth and other organisms.
c. E Horizon (Eluviated): The E horizon is leached of clay, minerals, and organic matter, resulting in a concentration of sand and silt particles. It is often found in older soils and forest soils.
d. B Horizon (Subsoil): The B horizon is enriched with minerals that have leached from the A or E horizons and accumulated here. It may contain clay, iron, aluminum, or other minerals.
e. C Horizon (Parent Material): The C horizon consists of the deposit at the Earth’s surface from which the soil developed. It is the layer where weathered rock fragments and minerals are found.
f. R Horizon (Bedrock): The R horizon is not considered soil but rather the underlying mass of rock, such as granite, basalt, quartzite, limestone, or sandstone. It serves as the parent material for some soils if it is close enough to the surface to weather.
O Horizon (Organic)
The O horizon is the uppermost horizon and consists mostly of organic matter, such as decomposing leaves, twigs, and other plant material. Its thickness varies in different soils and may be absent in some cases. The O horizon is important for soil fertility and water retention.
A Horizon (Topsoil)
The A horizon is the surface layer of the soil and is primarily composed of minerals from the parent material, along with incorporated organic matter. It is a fertile layer that supports plant growth and other organisms. The A horizon is typically darker in color than the underlying horizons due to the presence of organic matter.
E Horizon (Eluviated)
The E horizon is a subsurface horizon that has been leached of clay, minerals, and organic matter, resulting in a concentration of sand and silt particles. It is often found in older soils and forest soils. The E horizon is typically lighter in color than the A horizon due to the loss of organic matter and minerals.
B Horizon (Subsoil)
The B horizon is the subsoil layer and is enriched with minerals that have leached from the A or E horizons and accumulated here. It may contain clay, iron, aluminum, or other minerals. The B horizon is typically denser and less fertile than the A horizon.
C Horizon (Parent Material)
The C horizon consists of the deposit at the Earth’s surface from which the soil developed. It is the layer where weathered rock fragments and minerals are found. The C horizon is typically less weathered than the overlying horizons and may contain fragments of the parent rock.
R Horizon (Bedrock)
The R horizon is not considered soil but rather the underlying mass of rock, such as granite, basalt, quartzite, limestone, or sandstone. It serves as the parent material for some soils if it is close enough to the surface to weather.
Conclusion
Soil profiles provide valuable information about the soil’s properties, fertility, and history. By understanding the different horizons and their characteristics, soil scientists and land managers can make informed decisions about soil management and conservation practices.
References
- Soil Profile | Soils 4 Teachers (https://www.soils4teachers.org/soil-horizons)
- Soil Management (https://www.ctahr.hawaii.edu/mauisoil/a_profile.aspx)
- A Soil Profile | Natural Resources Conservation Service (https://www.nrcs.usda.gov/resources/education-and-teaching-materials/a-soil-profile)
FAQs
What is a soil profile?
A soil profile is a vertical section of the soil that displays all of its horizons. It extends from the soil surface to the parent rock material.
What are the major horizons commonly found in soil profiles?
The major horizons commonly found in soil profiles are the O horizon, A horizon, E horizon, B horizon, C horizon, and R horizon.
What is the O horizon and what does it consist of?
The O horizon is the uppermost horizon and consists mostly of organic matter, such as decomposing leaves, twigs, and other plant material.
What is the A horizon and what are its characteristics?
The A horizon is the surface layer of the soil and is primarily composed of minerals from the parent material, along with incorporated organic matter. It is a fertile layer that supports plant growth and other organisms.
What is the E horizon and how is it formed?
The E horizon is a subsurface horizon that has been leached of clay, minerals, and organic matter, resulting in a concentration of sand and silt particles. It is often found in older soils and forest soils.
What is the B horizon and what does it contain?
The B horizon is the subsoil layer and is enriched with minerals that have leached from the A or E horizons and accumulated here. It may contain clay, iron, aluminum, or other minerals.
What is the C horizon and what is its significance?
The C horizon consists of the deposit at the Earth’s surface from which the soil developed. It is the layer where weathered rock fragments and minerals are found. The C horizon is typically less weathered than the overlying horizons and may contain fragments of the parent rock.
What is the R horizon and why is it not considered soil?
The R horizon is the underlying mass of rock, such as granite, basalt, quartzite, limestone, or sandstone. It serves as the parent material for some soils if it is close enough to the surface to weather. The R horizon is not considered soil because it lacks the characteristics of soil, such as organic matter and developed structure.