Decomposition

Decomposers break complex organic matter down into inorganic substances such as carbon dioxide, water and nutrients. This is decomposition.

The earthworm is called the farmer's friend because it helps break down organic matter and loosens the soil.

Detritus, the raw material, is made of dead plant remains (leaves, bark, flowers) and dead animal remains, including fecal matter.

Fragmentation: detritivores such as the earthworm break detritus into smaller particles.

Leaching: water-soluble inorganic nutrients move down into the soil horizon and are precipitated as unavailable salts.

Catabolism: enzymes of bacteria and fungi break detritus down to simpler inorganic compounds. These three steps run at the same time on the detritus.

Humification forms humus, a dark, amorphous substance that resists microbes and decomposes very slowly. Being colloidal, it acts as a nutrient reservoir.

Mineralisation: some microbes degrade the humus further and release inorganic nutrients.

Decomposition mostly needs oxygen. It is slower when detritus is rich in lignin and chitin, and faster when it is rich in nitrogen and water-soluble substances such as sugars.

Of the climatic factors, temperature and soil moisture matter most, acting through soil microbes. Warm, moist conditions speed it up; low temperature and anaerobiosis slow it, so organic matter builds up.