ABSTRACT
The environment beneath the surface is less harsh and is suitable for insects and other soil animals, with plant material providing their foods. Micro-organisms make use of plant and animal residues eventually forming a resistant residue which is dark brown organic material called humus. The term soil organic matter is used for all the organic material in soil including humus. Litter inputs to soils are difficult to measure under natural vegetation as is the mass of root material which dies and becomes part of the soil organic matter each year. Laboratory measurements are normally made using a known mass of dry soil. In the field we often require values relating to a hectare of land. Clay is considered to stabilize organic matter by protecting it both physically and chemically. Although the chemistry of soil organic matter is complex its composition is broadly similar in all soils. The mass of living micro-organisms in a soil is known as the microbial biomass.
