Chapter 11: Problem 3

What are the different layers, or horizons, that compose a soil profile? What makes each one distinct from the others?

Short Answer

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Soil profile consists of several layers - O-Horizon (organic matter), A-Horizon (topsoil), E-Horizon (eluviation layer), B-Horizon (subsoil), C-Horizon (parent material), and R-Horizon (bedrock). Each of them, typically dark O-horizon rich in organic matter, darker A-horizon with a high biological activity, lighter E-horizon as a leaching zone, B-horizon rich in clay and leached substances, unweathered large-rock-heavy C-horizon, and inaccessible 'unweathered' R-horizon, has its own characteristics and roles in supporting plant and animal life.

Step by step solution

Identify the Soil Horizons

Start by identifying the different soil horizons. The distinguishable layers of soil typically from top to bottom are: O-Horizon (organic material), A-Horizon (topsoil), E-Horizon (eluviation layer), B-Horizon (subsoil), C-Horizon (parent material), and R-Horizon (bedrock).

Describe the O-Horizon

The O-Horizon is the topmost layer primarily composed of organic materials, including decomposed plants and animal matter. It is rich in humus, which gives it a dark color, and it's essentially productive for plant growth due to nutrients. In general, this layer is distinct thanks to its dark color and high organic matter content.

Describe the A-Horizon

The A-Horizon, also called topsoil, is the first layer beneath the O-Horizon. It is composed of minerals and organic matter mixed together, typically darker due to organic matter and high in biological activity. Roots of many plants can be found here which make this horizon crucial for plant life.

Describe the E-Horizon

The E-Horizon is the zone of leaching or eluviation where minerals and organic matter are leached down from this layer into the horizons below. It's a lighter layer due to the leaching process, and may not be present in all soil types.

Describe the B-Horizon

The B-Horizon, or subsoil, is the layer that receives the minerals and organic matter leeched from the above E-Horizon. This leads to its enrichment in clay, iron, aluminum oxides, and organic matter.

Describe the C-Horizon

The C-Horizon is the layer consisting mainly of larger pieces of rock, having less weathering, and is often called the parent material. This unweathered layer is closest to the parent material from which the soil was formed.

Describe the R-Horizon

The R-Horizon is the last layer, composed of consolidated bedrock. It's essentially the 'unweathered' rock layer and is mainly inaccessible to plant roots.

Conclusion

Every soil horizon features unique characteristics, such as colour, texture, structure, and content of organic matter, which make them distinct from one another and play different roles in supporting life.

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What are the different layers, or horizons, that compose a soil profile? What makes each one distinct from the others?

Short Answer

Step by step solution

Identify the Soil Horizons

Describe the O-Horizon

Describe the A-Horizon

Describe the E-Horizon

Describe the B-Horizon

Describe the C-Horizon

Describe the R-Horizon

Conclusion

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