Soil formation
Pedogenesis is the process of soil genesis regulated by place, environment, and history.
Soil formation, also known as pedogenesis, is the process of soil genesis as regulated by the effects of place, environment, and history. Biogeochemical processes act to both create and destroy order within soils, leading to the development of layers called soil horizons, distinguished by differences in color, structure, texture, and chemistry. These features occur in patterns of soil type distribution, forming in response to differences in soil forming factors. Pedogenesis is studied as a branch of pedology, the study of soil in its natural environment, and is important to understanding soil distribution patterns in current and past geologic periods.
- field
- Pedology
- known_for
- Process of soil genesis (pedogenesis) and the CLORPT factors
- key_factors
- Parent material, climate, topography, soil organisms, time
Lore & Background
Soil develops through a series of changes starting with weathering of freshly accumulated parent material. A variety of soil microbes feed on simple compounds released by weathering and produce organic acids and specialized proteins that contribute to mineral weathering. They also leave behind organic residues that contribute to humus formation. Plant roots with their symbiotic mycorrhizal fungi are also able to extract nutrients from rocks. New soils increase in depth by a combination of weathering and further deposition; in Sicily under Mediterranean climate the soil production rate due to weathering is approximately 1/10 mm per year. Gradually soil is able to support higher forms of plants and animals, starting with pioneer species and proceeding along ecological succession to more complex communities. As soils mature, they develop soil horizons as organic matter accumulates and mineral weathering and leaching take place.
Reader's Guide
Soil formation is influenced by at least five classic factors that are intertwined in the evolution of a soil: parent material, climate, topography (relief), soil organisms, and time. When reordered to climate, organisms, relief, parent material, and time, they form the acronym CLORPT. The mineral material from which a soil forms is called parent material, and typical soil parent mineral materials include quartz, calcite, feldspar, and mica. Parent materials are classified according to how they came to be deposited: residual materials weathered in place from primary bedrock, transported materials deposited by water, wind, ice or gravity, and cumulose material that is organic matter grown and accumulated in place. Most soils derive from transported materials moved many miles by wind, water, ice and gravity. Weathering of parent material takes the form of physical weathering (disintegration), chemical weathering (decomposition), and chemical transformation. Chemical weathering mainly results from the excretion of organic acids and chelating compounds by bacteria and fungi, and is thought to increase under greenhouse effect. Of the various chemical processes, hydrolysis and carbonation are the most effective, particularly in regions of high rainfall, temperature and physical erosion.
Did You Know?
- In Sicily under Mediterranean climate, the soil production rate due to weathering is approximately 1/10 mm per year.
- In the United States, as little as three percent of the soils are residual.
- Rocks that will decompose in a few years in tropical climates will remain unaltered for millennia in deserts.
- Chemical weathering mainly results from the excretion of organic acids and chelating compounds by bacteria and fungi.
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