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Despite agreement that organic matter is an essential soil component, terminological
confusion may result in inexact concepts of its role in controlling the chemical, physical
and biological processes. Humus, which is synthesized primarily in humification
process by microbes, is structurally very complex and resistant to degradation. It is
produced from non-humus material: litter, a whole series of decomposition products,
and identifiable constituents. Classifying soil organic matter into humus and non-humus
materials permits the systematization of reactions involving organic matter. Microbial
degradation of non-humus material releases plant nutrients and produces
polysaccharides that stabilize soil aggregates, thus improving conditions for root growth.
Antibiotics, vitamins and other active compounds affecting the biotic system can end
up into soil as byproducts of the microbial metabolism. Only a very small portion of
non-humus material is used as raw material for humus, whose importance is based on
physico-chemical properties. Through its high water holding capacity, humus can physically
control the mobility of compounds. Diverse functional groups participate in various
types of chemical reactions (ion exchange, complex formation, dissolution, physical
sorption of non-polar organic chemicals, etc). Similarly as in soil, humus acts as a
buffer in water bodies. However, in contrast to soil, in waters photochemical reactions
can enhance its degradation, thus leading to nutrient loadings and oxygen budget problems.
-
Hartikainen,
Department of Applied Chemistry and Microbiology, Box 27, 00014 University of Helsinkin, Finland
Sähköposti:
ei.tietoa@nn.oo
