solum

pedology

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July 16, 2026

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The term "solum" refers to the altered layer of soil above the parent material, encompassing the A and B horizons. Pedology is the scientific study of soils, examining their physical and chemical properties, the role of organisms, and their formation and mapping. Soil is structured into distinct layers called horizons, which develop from the combined actions of living organisms and percolating water.123

The main horizons include:
* O horizon: Organic matter, litter, and humus.
* A horizon: Mineral layer with accumulated humus.
* E horizon: Leached layer, lighter in color.
* B horizon: Accumulation of clay and humus from upper layers.
* C horizon: Unweathered parent material.
* R horizon: Consolidated bedrock.

The combined A, E, and B horizons are collectively known as the solum, representing the primary zone for soil-forming processes and the habitat for soil organisms.4

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soil
Soil horizons
…horizon sequence is called the solum (Latin: “floor”). The solum is the true seat of soil-forming processes and is the principal habitat for soil organisms. (Transitional layers, having intermediate properties, are designated with the two letters of the adjacent horizons, as shown in the table of soil horizon letter designations.)
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…horizon sequence is called the solum (Latin: “floor”). The solum is the true seat of soil-forming processes and is the principal habitat for soil organisms. (Transitional layers, having intermediate properties, are designated with the two letters of the adjacent horizons, as shown in the table of soil horizon letter designations.)
Read More