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Glossary

Soil Organic Matter (SOM)

Soil organic matter (SOM) is the totality of organic matter contained in the soil. SOM includes both living organic matter (biomass) and dead organic matter (humus). Mineral soils consist of 85 percent humus, about 10 percent of plant roots and 5 percent soil organisms (soil flora and fauna). Humus can be divided into humic and non-humic materials  so-called spreading materials. Humic substances are often divided into three sub-groups: humins, humic acids and fulvic acids. Furthermore, a distinction is made between particulate SOM (precipitated material), adsorbed SOM (substance bound to minerals or mineral soil) and dissolved organic matter.