Organic matter is a food and energy source for soil organisms and a source of plant nutrients.
Organic matter decomposition is a microbiological process that releases inorganic forms of nutrients such as nitrogen (N), phosphorus (P) and sulphur (S) which slowly become available for plant use.
The humus that develops as an intermediate product of these decompositions also acts as a store for nutrients. Soil organic carbon is generally highly correlated with total nitrogen. Therefore, the amount of N mineralisation (i.e. conversion of organic N compounds to ammonium-N) increases as soil organic carbon increases.
Organic matter provides active absorption sites for the deactivation of organic chemicals such as pesticides, particularly herbicides. Micro-organisms associated with soil organic matter may also rapidly decompose soil-applied organic chemicals.
Adding organic matter to the soil contributes a certain level of sequestration of carbon from the atmosphere. This is currently an active area of research by scientists concerned with increasing the carbon content of soils to mitigate the adverse effects of climate change and to potentially utilise it in emission trading schemes.
See other functions of organic matter