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Refers to the suppression of growth of one plant species by another due to the release of toxic substances.


Conversion of organically bound N into ammonium-N by soil biota.


A tool that uses a constant head of water to measure the rate of water movement in a saturated soil, and thus estimates saturated hydraulic conductivity.


Without oxygen. Anaerobic organisms, including some soil bacteria, need oxygen-free environments such as saturated soils. Facultative anaerobes can function as either aerobes or anaerobes depending on environmental conditions. See aerobic.

Anaerobic soil

Soil characterized by the absence of oxygen molecules (Fe3+, Mn4+, NO3-, SO42-


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).


Generated by humans. Used to indicate soil conditions, disturbances, or stresses that are created by people.


is when separate elements produce a decreased effect when acting together than would be produced if they acted separately.

Apparent efficiency

Yield increase of a crop per unit of nutrient applied (kg per kg) in addition to the yield of an unfertilized control.

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