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Clay cannot be resolved by optical microscopes as its particles are 0.002 mm (7.9 × 10 −5 in) or less in diameter and a thickness of only 10 angstroms (10 −10 m). [ 16 ] [ 17 ] In medium-textured soils, clay is often washed downward through the soil profile (a process called eluviation ) and accumulates in the subsoil (a process called ...
The term comes from humus, which in turn comes from the Latin word humus, meaning "soil, earth". [1] Humic substances represent the major part of organic matter in soil , peat , coal , and sediments , and are important components of dissolved natural organic matter (NOM) in lakes (especially dystrophic lakes ), rivers, and sea water .
The soil production rate due to weathering is approximately 1/10 mm per year. [5] New soils can also deepen from dust deposition. Gradually soil is able to support higher forms of plants and animals, starting with pioneer species and proceeding along ecological succession to more complex plant and animal communities. [6]
Soil aeration maintains oxygen levels in the plants' root zone, needed for microbial and root respiration, and important to plant growth. Additionally, oxygen levels regulate soil temperatures and play a role in some chemical processes that support the oxidation of elements like Mn 2+ and Fe 2+ that can be toxic.
Soil morphology is the branch of soil science dedicated to the technical description of soil, [1] particularly physical properties including texture, color, structure, and consistence. Morphological evaluations of soil are typically performed in the field on a soil profile containing multiple horizons .
Soil physics is the study of soil's physical properties and processes. It is applied to management and prediction under natural and managed ecosystems . Soil physics deals with the dynamics of physical soil components and their phases as solids , liquids , and gases .
Soil microbial communities experience shifts in the diversity and composition during dehydration and rehydration cycles. [5] Soil moisture affects carbon cycling a phenomenon known as Birch effect. [6] [7] Temperature variations in soil are influenced by factors such as seasonality, environmental conditions, vegetation, and soil composition.
Soil is used in agriculture, where it serves as the anchor and primary nutrient base for plants. The types of soil and available moisture determine the species of plants that can be cultivated. Agricultural soil science was the primeval domain of soil knowledge, long time before the advent of pedology in the 19th century.