Q:

What are the main soil layers?

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Quick Answer

The distinct soil layers, or horizons, are organic matter, humus, topsoil, the eluviated layer, subsoil, regolith and bedrock. The main horizons are also referred to as master horizons and are often designated and recognized using the letters O, P, A, E, B, C and R, respectively.

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Full Answer

Not all soil profiles comprise all of the listed layers; soil profiles differ based on location. Each of the horizons varies in thickness and has a set of unique characteristics that differentiate it from the other layers. The layers are identified based on color, structure, texture or chemical composition. For example, while A horizon is dark, coarse and home to earthworms and fungi, R horizon contains hard bedrock that cannot be unearthed with human hands. Identifying the soil horizons helps reveal certain characteristics about the soil that may be essential in establishing suitable land uses.

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    Residual soil is the accumulation of soil caused by the erosion of underlying bedrock, while transported soil is soil deposited into new regions after erosion. Both types of soil are formed from the chemical and mechanical weathering of rock materials.

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    What are some interesting facts about soil?

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    What are the four layers of soil?

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    Which soil layer contains the most humus?

    A:

    The O horizon soil layer contains the most humus. This layer is the topmost layer of most types of soil. The O horizon layer is primarily composed of decomposed plant litter and humus.

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