Decomposition

Decomposition is the process by which decomposers break down complex organic matter into simpler inorganic substances such as carbon dioxide, water and mineral nutrients. The raw material for this process is detritus — the dead remains of plants and animals, including fecal matter. Decomposition proceeds through several distinct but simultaneously operating steps: fragmentation, leaching, catabolism, humification and mineralization.

Fragmentation is carried out by detritivores such as earthworms, which physically break detritus down into smaller particles, increasing the surface area available to microbes. Leaching is the process by which water-soluble inorganic nutrients percolate down through the soil profile and become precipitated as salts that are, for the time being, unavailable to plants. Catabolism is the chemical breakdown of detritus by bacterial and fungal enzymes into simpler inorganic substances. Humification then leads to the accumulation of humus — a dark-coloured, amorphous, colloidal organic substance that resists further microbial attack and decomposes only very slowly; because it is colloidal, humus also serves as a reservoir of nutrients, and its formation improves the soil's texture and increases its water-holding capacity. Finally, mineralization is the further breakdown of this humus by some microbes, releasing inorganic nutrients back into the soil for renewed uptake by plants. …