Oxidation

A chemical weathering process, which is a reaction process in which minerals, or elements, gain an oxygen molecule, through the exchange of electrons during the process of combining with oxygen. A common example is that of iron reacting with oxygen to form rust (iron oxide), with decomposition of organic matter also being an oxidation process.

The typical process would occur as follows:
• Oxygen in the soil profile reacts with minerals or elements in the soil. This can be enhanced by the activities of oxidising soil micro-organisms.
• Chemical changes occur, with the result being the forming of new compounds, for example Fe(II), Ferrous oxide, to Fe(III), Ferric oxide.
• With the chemical changes that occur in the oxidation process, the release of ions into a soil solution can affect soil pH, by either increasing or decreasing soil acidity. For example, with the oxidation of sulphur containing compounds, released sulphur dioxide (SO2) can react with water to form sulphuric acid (H2SO4) contributing to making a soil more acidic.

Oxidation contributes to soil formation and soil fertility, with influencing factors being the availability of soil oxygen, soil moisture content, temperature, and the chemical composition of a soil as well as presence and extent of organic matter and soil micro-organisms.