Soil organic matter is carbon-rich material that includes plant, animal, and microbial residue in various stages of decomposition. Live soil organisms and plant roots are part of the carbon pool in soil but are not considered soil organic matter until they die and begin to decay. The quantity and composition of soil organic matter vary significantly among major ecosystems. Soil in arid, semiarid, and hot, humid regions commonly has less organic matter than soil in other environments. The total content of organic matter ranges from less than 0.5 to more than 8 percent in the surface layer of rangeland soils. Soil organic matter includes three main components (table 1). The light fraction is more biologically active than the other two [...]
Summary
Soil organic matter is carbon-rich material that includes
plant, animal, and microbial residue in various stages of
decomposition. Live soil organisms and plant roots are part of
the carbon pool in soil but are not considered soil organic matter
until they die and begin to decay.
The quantity and composition of soil organic matter vary
significantly among major ecosystems. Soil in arid, semiarid,
and hot, humid regions commonly has less organic matter than
soil in other environments. The total content of organic matter
ranges from less than 0.5 to more than 8 percent in the surface
layer of rangeland soils.
Soil organic matter includes three main components (table 1).
The light fraction is more biologically active than the other two
and includes relatively fresh plant fragments. Physically
protected organic matter is locked within aggregates of mineral
particles, where it is protected from microbial decomposition.
Chemically stable organic matter gives soil its dark color and is
generally the largest pool of organic matter in soil. Physically
protected organic matter may also be chemically stable.