Growing and reproducing are the primary activities of all living organisms. As individual plants and soil organisms work to survive, they depend on interactions with each other. By-products from growing roots and plant residue feed soil organisms. In turn, soil organisms support plant health as they decompose organic matter, cycle nutrients, enhance soil structure, and control the populations of soil organisms including crop pests. 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.