THE FOOD WEB Soil organic matter is the storehouse for the energy and nutrients used by plants and other organisms. Organic matter is many different kinds of compounds some more useful to organisms than others. In general, soil organic matter is made of roughly equal parts humus and active organic matter. Active organic matter is the portion available to soil organisms. Bacteria tend to use simpler organic compounds, such as root exudates or fresh plant residue.
Fungi tend to use more complex compounds, such as fibrous plant residues, wood and soil humus.
As soil organic matter levels rise, soil organisms play a role in its conversion to humus a relatively stable form of carbon sequestered in soils for decades or even centuries. Here are terms used to describe different types of organic matter. Bacteria, fungi, nematodes, protozoa, earthworms, arthropods, and living roots. Detritivores are organisms that feed on such material. The active fraction changes more quickly than total organic matter in response to management changes.