Organic matter or organic material, natural organic matter, NOM is matter
composed of organic compounds that has come from the remains of organisms such
as plants and animals and their waste products in the environment. Organic
molecules can also be made by chemical reactions that don't involve life. Basic
structures are created from cellulose, tannin, cutin, and lignin, along with
other various proteins, lipids, and carbohydrates. It is very important in
the movement of nutrients in the environment and plays a role in water
retention on the surface of the planet. Formation
Living organisms are composed of organic compounds. In life they secrete or
excrete organic materials into their environment, shed body parts such as
leaves and roots and after the organism dies, its body is broken down by
bacterial and fungal action. Larger molecules of organic matter can be
formed from the polymerization of different parts of already broken down
matter. The composition of natural organic matter depends on its origin,
transformation mode, age, and existing environment, thus its
bio-physico-chemical functions vary with different environments.
Natural ecosystem functions Organic matter is present throughout the
ecosystem. After degrading and reacting, it can move into soil and mainstream
water via waterflow. Organic matter provides nutrition to living organisms.
Organic matter acts as a buffer in aqueous solution to maintain a neutral
pH in the environment. The buffer acting component has been proposed to be
relevant for neutralizing acid rain. Source cycle
A majority of organic matter not already in the soil comes from groundwater. When
the groundwater saturates the soil or sediment around it, organic matter can
freely move between the phases. Groundwater has its own sources of
natural organic matter also: "organic matter deposits, such as
kerogen and coal soil and sediment organic matter
organic matter infiltrating into the subsurface from rivers, lakes, and
marine systems" Note that one source of groundwater
organic matter is soil organic matter and sedimentary organic matter. The
major method of movement into soil is from groundwater, but organic matter
from soil moves into groundwater as well. Most of the organic matter in
lakes, rivers, and surface water areas comes from deteriorated material in the
water and surrounding shores. However, organic matter can pass into or out of
water to soil and sediment in the same respect as with the soil.
= Importance of the cycle= Organic matter can migrate through soil,
sediment, and water. This movement enables a cycle. Organisms decompose
into organic matter, which can then be transported and recycled. Not all
biomass migrates, some is rather stationary, turning over only over the
course of millions of years. Soil organic matter
The organic matter in soil derives from plants and animals. In a forest, for
example, leaf litter and woody material falls to the forest floor. This is
sometimes referred to as organic material. When it decays to the point in
which it is no longer recognizable it is called soil organic matter. When the
organic matter has broken down into a stable substance that resist further
decomposition it is called humus. Thus soil organic matter comprises all of the
organic matter in the soil exclusive of the material that has not decayed.
One of the advantages of humus is that it is able to withhold water and
nutrients, therefore giving plants the capacity for growth. Another advantage
of humus is that it helps the soil to stick together which allows nematodes,
or microscopic bacteria, to easily decay the nutrients in the soil.
There are several ways to quickly increase the amount of humus. Combining
compost, plant or animal materials/waste, or green manure with
soil will increase the amount of humus in the soil.
Compost: decomposed organic material. Plant and animal material and waste:
dead plants or plant waste such as leaves or bush and tree trimmings, or
animal manure. Green manure: plants or plant material
that is grown for the sole purpose of being incorporated with soil.
These three materials supply nematodes and bacteria with nutrients for them to
thrive and produce more humus, which will give plants enough nutrients to
survive and grow. = Factors controlling rates of
decomposition= Environmental factors
1. Aeration 2. Temperature
3. Soil Moisture 4. Soil pH
Quality of added residues 1. Size of organic residues
2. C/N of organic residues Rate of decomposition of plant residues,
in order from fastest to slowest decomposition rates:
1. Sugars, starches, simple proteins 2. Hemicellulose
3. Cellulose 4. Fats, waxes, oils, resins
5. Lignin, phenolic compounds = Priming effect=
The priming effect is characterized by intense changes in the natural process
of soil organic matter turnover, resulting from relatively moderate
intervention with the soil. The phenomenon is generally caused by either
pulsed or continuous changes to inputs of fresh organic matter. Priming effects
usually result in an acceleration of mineralization due to a trigger such as
the FOM inputs. The cause of this increase in decomposition has often been
attributed to an increase in microbial activity resulting from higher energy
and nutrient availability released from the FOM. After the input of FOM,
specialized microorganisms are believed to grow quickly and only decompose this
newly added organic matter. The turnover rate of SOM in these areas is at least
one order of magnitude higher than the bulk soil.
Other soil treatments, besides organic matter inputs, which lead to this
short-term change in turnover rates, include "input of mineral fertilizer,
exudation of organic substances by roots, mere mechanical treatment of soil
or its drying and rewetting." Priming effects can be either positive
or negative depending on the reaction of the soil with the added substance. A
positive priming effect results in the acceleration of mineralization while a
negative priming effect results in immobilization, leading to N
unavailability. Although most changes have been documented in C and N pools,
the priming effect can also be found in phosphorus and sulfur, as well as other
nutrients. Löhnis was the first to discover the
priming effect phenomenon in 1926 through his studies of green manure
decomposition and its effects on legume plants in soil. He noticed that when
adding fresh organic residues to the soil, it resulted in intensified
mineralization by the humus N. It was not until 1953, though, that the term
priming effect was given by Bingeman in his paper titled, The effect of the
addition of organic materials on the decomposition of an organic soil.
Several other terms had been used before priming effect was coined, including
priming action, added nitrogen interaction, extra N and additional N.
Despite these early contributions, the concept of the priming effect was widely
disregarded until about the 1980s-1990s. The priming effect has been found in
many different studies and is regarded as a common occurrence, appearing in
most plant soil systems. However, the mechanisms which lead to the priming
effect are more complex then originally thought, and still remain generally
misunderstood. Although there is a lot of uncertainty
surrounding the reason for the priming effect, a few undisputed facts have
emerged from the collection of recent research:
The priming effect can arise either instantaneously or very shortly after
the addition of a substance is made to the soil.
The priming effect is larger in soils that are rich in C and N as compared to
those poor in these nutrients. Real priming effects have not been
observed in sterile environments. The size of the priming effect increases
as the amount of added treatment to the soil increases.
Recent findings suggest that the same priming effect mechanisms acting in soil
systems may also be present in aquatic environments, which suggests a need for
broader considerations of this phenomenon in the future.
Decomposition One suitable definition of organic
matter is biological material in the process of decaying or decomposing, such
as humus. A closer look at the biological material in the process of
decaying reveals so-called organic compounds in the process of breaking up.
The main processes by which soil molecules disintegrates are by bacterial
or fungal enzymatic catalysis. If bacteria or fungi were not present on
Earth, the process of decomposition would have proceeded much slower.
Organic chemistry Measurements of organic matter generally
measure only organic compounds or carbon, and so are only an approximation
of the level of once-living or decomposed matter. Some definitions of
organic matter likewise only consider "organic matter" to refer to only the
carbon content, or organic compounds, and do not consider the origins or
decomposition of the matter. In this sense, not all organic compounds are
created by living organisms, and living organisms do not only leave behind
organic material. A clam's shell, for example, while biotic, does not contain
much organic carbon, so may not be considered organic matter in this sense.
Conversely, urea is one of many organic compounds that can be synthesized
without any biological activity. Very little is currently known about
natural organic material. Scientists are unable to crystallize it. This is
important because once you can crystallize the material, it can be
isolated and studied with x-ray crystallography. This method is standard
for determining unknown compounds. Organic matter has not been
characterized either and no unique structure is known. The best way to
characterize organic matter is by discovering chemical, physical, and
thermodynamic properties of the matter. Analytical techniques are currently
being discovered to allow this to happen. The only information scientists
have is that organic matter is heterogeneous and very complex.
Generally, organic matter, in terms of weight, is:
45-55% carbon 35-45% oxygen
3-5% hydrogen 1-4% nitrogen
The molecular weights of these compounds can vary drastically, depending on if
they repolymerize or not, from 200-20,000 amu. It is also important to
know that 10-35% of the carbon present forms aromatic rings. These rings are
very stable due to resonance stabilization, so they are difficult to
break down. The aromatic rings are also susceptible to electrophilic and
nucleophilic attack from other electron-donating or electron-accepting
material, which explains the possible polymerization to create larger
molecules of organic matter. There are also reactions that occur with
organic matter and other material in the soil to create compounds never seen
before. Unfortunately, it is very difficult to characterize these because
so little is known about natural organic matter in the first place. Research is
currently being done to figure out more about these new compounds and how many
of them are being formed. Organic matter in water
= Water purification= The same capability of natural organic
matter that helped with water retention in soil creates problems for current
water purification methods. In water, organic matter can still bind to metal
ions and minerals. These bound molecules are not necessarily stopped by the
purification process, but do not cause harm to any humans, animals, or plants.
However, because of the high level of reactivity of organic matter,
by-products that do not contain nutrients can be made. These by-products
can induce biofouling, which essentially clogs water filtration systems in water
purification facilities, as the by-products are larger than membrane
pore sizes. This clogging problem can be treated by chlorine disinfection, which
can break down residual material that clogs systems. However, chlorination can
form disinfection by-products. = Potential solutions=
Water with organic matter can be disinfected with ozone-initiated radical
reactions. The ozone has very strong oxidation characteristics. It can form
hydroxyl radicals when it decomposes, which will react with the organic matter
to shut down the problem of biofouling. = False positives=
Many water quality groups, such as the North Carolina State University Water
Quality Group, believe that having too much organic material will cause
deoxygenation and essentially remove oxygen from the water. Although organic
material, which consists of many hydrocarbon and cyclic carbon chains, is
susceptible to attack by oxygen, it would be sterically unfavorable to
attach oxygens to every single carbon. Of course, there are exceptions, such as
varying the temperature at which these reactions occur. As the temperature
becomes much higher, there is a better chance that an unfavorable reaction will
occur because molecules move around faster increasing the randomness of the
system. Vitalism
The equation of "organic" with living organisms comes from the now-abandoned
idea of vitalism that attributed a special force to life that alone could
create organic substances. This idea was first questioned after the artificial
synthesis of urea by Friedrich Wöhler in 1828.
See also Biofact
Biomass Detritus
Humus Organic geochemistry
Sedimentary organic matter Total organic carbon
Compare with: Biological tissue
Biomolecule Biotic material
Cellular component Organic production
References Bibliography
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