Organic Matter

Soil organic matter is the fraction of the soil that consists of plant or animal tissue in various stages of breakdown (decomposition) Soil organic matter takes only a few percent of most soils, but it has a great deal of influence on soil properties and agricultural productivity . In the production of a fertile soil, organic substances play a direct part as they are the sources of plant nutrients which are liberated in available forms during mineralization .

Fromation Source

Plant residues and microbial biomass

Microbial biomass (bacteria and fungi) is a measure of the mass of the living component of soil organic matter. The microbial biomass decompose plant and animal residues and soil organic matter to release carbon dioxide and plant available nutrients. Farming systems that return plant residues (e.g. no-tillage) tend to increase the microbial biomass. Soil properties such as pH, clay, and the availability of organic carbon all influence the size of the microbial biomass.

Detritus

Detritus is living organic matter composed of leaves and other plant parts, animal remains, waste products, and other organic debris that falls onto the soil or into bodies of water from surrounding terrestrial communities. Microorganisms (such as bacteria or fungi) break down detritus, and this microorganism-rich material is eaten by invertebrates, which are in turn eaten by vertebrates. Many freshwater streams have detritus rather than living plants as their energy base.