What is soil organic matter?

Soil organic matter (SOM) is the mix of plant and animal matter in different stages of decay. Soil organic matter plays a key role in biological, physical, and chemical function in soil. Soil organic matter is the organic component of soil, consisting of three primary parts including small (fresh) plant residues and small living soil organisms, decomposing (active) organic matter, and stable organic matter (humus). Organic matter serves as a reservoir of nutrients and water in the soil, aids in reducing compaction and surface crusting, and increases water infiltration into the soil.