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Uptake of matter or energy by a substance.

Accelerated erosion

The erosion that exceeds the normal geologic erosion and becomes destructive. It occurs when people disturb the soil or the natural vegetation by cutting forests, overgrazing, ploughing hillsides, recreational activity (e.g., ATV vehicle uses), indiscriminate (arbitrary) burning, or construction of roads and buildings.


Process whereby soil becomes acid (pH < 7) because acid parent material is present or in regions with high rainfall, where soil leaching occurs.  Acidification can be accelerated by human activities (use of fertilisers, deposition of industrial and vehicular pollutants).

Aerated soil

An aerated soil is a soil with a good movement of air through the soil structure. The opposite is a wet waterlogged soil, where the soil pores are filled with water.


Soil aggregate consisting of two or more soil particles bound together by various forces.


Process whereby primary soil particles (sand, silt, clay) are bound together, usually by natural forces and substances derived from root exudates and microbial activity. Soil aggregates are arranged to form soil peds, units of soil structure, classified by size, shape (platy, prismatic, columnar, angular, subangular, blocky, granular…) and grade (single-grain, massive, weak, moderate, strong). From an agronomical point of view, the most important soil aggregates are in range 3 - 1 mm.

Anaerobic soil

Soil characterized by the absence of oxygen molecules (Fe3+, Mn4+, NO3-, SO42- are secondary electrons acceptors).


Particle with a negative charge. See also ion, cation.

Anion exchange capacity

Sum of exchangeable anions that a soil can adsorb. Usually expressed as centimoles, or millimoles, of charge per kilogram of soil (or of other adsorbing material such as clay).


An underground layer of permeable rock, sediment, or soil that yields water

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