mus absorbs heat from the sun,
thereby improving soil temperature
for plant growth and microbial activity under cooler climatic conditions.
Important functions of organic
matter:
Some of the most important functions of organic matter in the soil
are:
•It increases soil fertility as it retains
cations and conserves nutrients in
organic forms and slowly releases
required nutrients for plant uptake
and growth.
• It binds soil particles together; the
cementing and aggregation functions improving soil structure and
aeration.
• It acts as a sponge in the soil, retaining soil moisture. Soils with
high organic matter content can
hold more water than those low in
organic matter.
• It provides food for microorganisms living in the soil.
Decomposition is the general process whereby dead organic materials are transformed into simpler
states with the concurrent release
of energy and their contained biological nutrient and other elements
in inorganic forms. Such forms are
directly assimilable by microorganisms and plants, and the remaining soil organic matter may be
stabilized through physical and
chemical processes or further decomposed (Lavelle and Spain,
2001). These transformations of
dead organic materials into assimilable forms involve the simultaneous and complementary processes
of mineralization and humification:
Mineralization is the process
through which the elements
contained in organic form within biological tissues are converted to inorganic forms such as
nitrate, phosphate and sulphate
ions.
Humification is an anabolic process where organic molecules
are condensed into degradationresistant organic polymers,
which may persist almost unaltered for decades or even centuries.
Decomposition is essentially a biological process. Nutrients taken up
by plants are derived largely from
the decomposition process. Microorganisms are by far the major contributors to soil respiration and are
responsible for 80-95 percent of the
total carbon dioxide (CO2) respired
and, consequently of the organic C
respired. Therefore, decomposition
is a process determined by the interactions of three factors: organisms, environmental conditions
(climate and minerals present in the
soil); and the quality of the decomposing resources. These factors op-
erate at different spatial and temporal scales.
Living organisms are made up of
thousands of different compounds.
Thus, when organisms die, there
are thousands of compounds in the
soil to be decomposed. As these
compounds are decomposed, the
organ