ABSTRACT
The redox (reduction-oxidation) potential is one of the primary factors controlling chemical reactions in soils. Well-drained soils are typically considered well aerated and hence oxidizing, whereas waterlogging is considered to produce reducing conditions. However, this generalization ignores the dynamic and heterogeneous nature of soil systems. Oxygen depletion can occur wherever oxygen consumption by plant roots and microorganisms exceeds its rate of supply. This condition is encountered in a range of situations within well-drained soils, for example, inside aggregates, in compacted subsoils, when organic wastes are applied to land, and within plant rhizospheres. In view of the ubiquitous nature of changing redox conditions in soil, the potential for redox reactions to alter trace metal chemistry must be considered.
