The dark, loamy, organic portion of the soil
remaining after prolonged microbial decomposition.
Humus is a general
term used to indicate the more or less complex organic substance
resulting from the decomposition of plant and animal residues in
a process called humification that forms the organic portion of
soil. It is a dark coloured (brown or black) stable form of
organic matter that remains after most of plant or animal
residues have decomposed and mineralized. Generally, the
decomposition has proceeded sufficiently to make it amorphous
(it has decomposed sufficiently so that the source material is
no longer recognizable) and relatively stable (it resists
further decomposition because it is chemically
protected/resistant). Humus mixes with top layers of soil (rock
particles), supplies some of the nutrients needed by plants and
increases acidity of soil (many inorganic nutrients are more
soluble under acidic conditions, become more available). Humus
modifies soil texture, coating mineral particles and holding
them together; creates loose, crumbly texture, that allows water
to soak in and nutrients retained; permits air to be
incorporated into soil. Humus is extremely important to the
fertility of soils in both a physical and chemical sense and is
a major source of nutrients for soil organisms and plants.
Often incorrectly referred to as any decomposing organic
material including sawdust, ground bark and manure.
To humify (Transitive
& intransitive verb humifies,
To make or turn into humus.
The process of the formation of
The process of
decomposition whereby organic material is humified and becomes
and converted to humic substances through biochemical and
Also used to evaluate the degree of decomposition of organic
matter. Three degrees of humification are recognized in organic
soil materials: fibric, hemic and sapric.