ORGANIC MATTER, HUMUS, HUMATE, HUMIC ACID,
FULVIC ACID, AND HUMIN:
Dr. Robert E. Pettit
Emeritus Associate Professor, Texas A&M
University
INTRODUCTION
Humic substances, such as those listed in
the above title, play a vital role in soil
fertility and plant nutrition. Plants grown
on soils which contain adequate humin, humic
acids (Has), and fulvic acids (Fas) are less
subject to stress, are healthier, produce
higher yields; and the nutritional quality
of harvested foods and feeds are superior.
The value of humic substances in soil
fertility and plant nutrition relates to the
many functions these complex organic
compounds perform as a part of the life
cycle on earth. The life-death cycle
involves a recycling of the carbon
containing structural components of plants
and animals - through the soil and air - and
back into the living plant
Man became distracted from the importance of
organic compound cycling when it was
discovered that soluble acidic based N-P-K
“fertilizers” could stimulate plant growth.
Large industrial concerns took advantage of
the N-P-K discovery to market industrially
processed “fertilizers” from mineral
deposit. Continued use of these acidic
fertilizers in the absence of adequate humic
substance (in the soil) has caused many
serious sociological and ecological
problems. Man needs to reconsider his
approach to fertilization techniques by
giving higher priority to soil humus.
The urgency to emphasize the importance of
humic substances and their value as
fertilizer ingredients has never been more
important than it is today. All those
concerned about the ability of soils to
support plant growth need to assist in
educating the public. Humic substances are
recognized by most soil scientists and
agronomists as the most important component
of a healthy fertile soil. To illustrate how
humic substances function, the following
summary, based on published scientific data,
has been prepared as a guide for an
educational program. In addition, by
understanding how these carbon containing
substances function, professionals will have
a solid foundation on which to design
environmentally acceptable sustainable
agriculture programs.
DESCRIPTION OF TERMS USED IN THE SUMMARY
A brief discussion of several important
terms will help clarify to the reader the
significance of humic substances, and how
scientists have subdivided and described
specific extracts from these substances. Key
features of these extracts have been
discovered as agriculturists have worked to
understand the structural and functional
properties of humic substances.
ORGANIC MATTER - Organic matter is defined
as a grouping of carbon containing compounds
which have originated from living beings and
been deposited on or within the earth’s
structural components. Soil organic matter
includes the remains of all plant and animal
bodies which have fallen on the earth’s
surface or been purposely applied by man in
the form of organically synthesized
pesticides. A fertile soil should contain
from 2-8 percent organic matter; most soils
contain less than 2%. In acid, leached
soils, which are often sandy, substantial
portions of the organic matter is in the
form of plant debris and fulvic acids (FAs).
In neutral and alkaline soils a large
percentage of the organic matter is in the
form of humic acids (HAs) and humin.
When organic matter is burned, there remains
a residual ash. The residual ash is composed
of the minerals, trace elements required by
plants and animals during their normal
growth processes. Thus organic matter
contains mineral elements required by plants
An accurate measurement of the soil would be
helpful in monitoring soil fertility.
Currently the best extractant for removing
organic matter from a soil is 0.5 normal
sodium hydroxide (NaOH) (working under N2).
The second best extractant is sodium
pyrophosphate decahydrate (Na4P2O7 10H2O (pH
9.8)). Neither one of these extractants is
able to remove all of the organic matter
from a soil sample. Obviously since these
chemicals are the best known it is
impossible to determine the exact amount of
organic matter present within a soil. In
reality soil organic matter is not a
measurable soil component. The organic
matter content of a soil sample, reported on
soil tests, is only an estimate. The organic
carbon content of a soil can be measured and
would be a much more valuable indication of
the potential humic-chemistry of a soil. The
soil’s carbon content would be a desirable
part of a soil test report.
HUMUS - Humus is defined as a brown to black
complex variable of carbon containing
compounds not recognized under a light
microscope as possessing cellular
organization in the form of plant and animal
bodies. Humus is separated from the
non-humic substances such as carbohydrates
(a major fraction of soil carbon),fats,
waxes, alkanes, peptides, amino acids,
proteins, lipids, and organic acids by the
fact that distinct chemical formulae can be
written for these non-humic substances. Most
small molecules of non-humic substances are
rapidly degraded by microorganisms within
the soil. In contrast soil humus is slow to
decompose (Degrade) under natural soil
conditions. When in combination with soil
minerals soil humus can persist in the soil
for several hundred years. Humus is the
major soil organic matter component, making
up 65% to 75% of the total. Humus assumes an
important role as a fertility component of
all soils, far in excess of the percentage
contribution it makes to the total soil
mass.
HUMIC SUBSTANCES - humic substances are the
components of humus and as such as high
molecular weight compounds that together
form the brown to black hydrophilic,
molecularly flexible, polyelectrolytes
called humus. Many of the components of
humus are heterogeneous, relatively large
stable organic complexes. They function to
give the soil structure, porosity, water
holding capacity, cation and anion exchange,
and are involved in the chelation of mineral
elements. The elemental analysis of humic
substances reveals that they are primarily
composed of carbon, oxygen, hydrogen,
nitrogen, and sulfur in complex carbon
chains (aliphatic components that make up
approximately 40% - 50% of the total)
C-C-C-C and 4, 5, and 6 member carbon rings
(aromatic components that make up 35% - 60%
of the total) with C-C, C-N, and C=O
groupings.
Preliminary understandings about how humic
substances are formed is based on 4
published theories: (1) Lignin
modifications, (2) Quinone -Amino Acid
Interaction, (3) Microbial Synthesis of
Aromatics, and (4) The Mallard Reaction (a
sugar - amino acid reaction sequence). Each
theory describes complicated biotic and
abiotic reactions in which a variety of
organic compounds, such as phenolic
compounds (e.g. lignins), complex
carbohydrates, and nitrogenous substances
are resynthesized to form large complex
polymers. In order for these polymerization
reactions to proceed, inorganic mineral
catalysts must be present. Therefore, the
availability of trace minerals is a
requirement for the formation of humic
substance. The extreme variability in the
molecular features of humic substances
relates back to the precursor compounds and
the environmental conditions under which the
humic substances formed.
Humic substances have been shown to contain
a wide variety of molecular components. Some
typical components are: polysacharides:
fatty acids: polypeptides; lignins; esters:
phenols; ethers; carbonyls; quinones;
lipids; peroxides; various combinations of
benzene, acetal, ketal, and lactol, and
furan ringed compounds; and aliphatic
(carbon chains) compounds. The oxidative
degradation of some humic substances
produces aliphatic, phenolic, and benzene
carboxylic acids in addition to n-alkanes
and n-fatty acids. The major phenolic acids
released contain approximately 3 hydroxyl
(-OH) groups and between 1 and 5 carboxyl
(-COOH) groups.
Humic substances can be subdivided into
three major fractions (1) HUMIN, (2) HUMIC
ACIDS (Has), and (3) FULVIC ACIDS (Fas).
These sub-divisions are arbitrarily based on
the solubility of each fraction in water
adjusted to different acid - alkaline (pH
levels) conditions. Some of the major
features of humic substances are summarized
in Figure 1.
HUMINS - Humins are that fraction of humic
substances which are not soluble in alkali
(high pH) and are not soluble in acid (low
pH). Humin are not soluble in water at any
pH. Humin complexes are considered
macro-organic (very large) substances
because their molecular weights (MW) range
from approximately 100,000 to 10,000,000. In
comparison the molecular weights of
carbohydrates (complex sugars) range from
approximately 500 to 100,000. The chemical
and physical properties of humins are only
partially understood. Humins present within
the soil is the most resistant to
decomposition (slow to breakdown) of all the
humic substances. Some of the main functions
of humins within the soil are to improve the
soils water holding capacity, to improve
soil structure, to maintain soil stability,
to function as a cation exchange system, and
to generally improve soil fertility. Because
of these important functions humin is the
key component of fertile soils.
HUMIC ACIDS - Humic acids (Has) comprise a
mixture of weak aliphatic (carbon chains)
and aromatic (carbon rings) organic acids
which are not soluble in water under acid
conditions but are soluble in water under
alkaline conditions. Humic acids consist of
that fraction of humic substances that are
precipitated from aqueous solution when the
pH is decreased below 2.
Humic acids (HAs) are termed polydisperse
because of their variable chemical features.
From a three dimensional aspect these
complex carbon containing compounds are
considered to be flexible linear polymers
that exist as random coils with cross-linked
bonds. On average 35% of the humic acid (HA)
molecules are aromatic (carbon rings), while
the remaining compounds are in the form of
aliphatic (carbon chains) molecules. The
molecular size of humic acids (HAs) range
from approximately 10,000 to 100,000. Humic
acid (HA) polymers readily bind clay
minerals to form stable organic-clay
complexes. Peripheral pores in the plant are
capable of accommodating (binding) natural
and synthetic organic chemicals in a lattice
(clathrate) type arrangement.
Humic acids (HAs) readily form salts with
inorganic trace mineral elements. An
analysis of extracts of naturally occurring
humic acids (HAs) will reveal the presence
of over 60 different mineral elements
present. These trace elements are bound in
humic acid molecules in a form that can be
readily utilized by various living
organisms. As a result humic acids (HAs)
function as important ion-exchange and
metal-complexing (chelating) systems.
FULVIC ACIDS - fulvic acids (FAs) are a
mixture of weak aliphatic and aromatic
organic acids which are soluble in water at
all pH conditions (acidic, neutral and
alkaline). Their composition and shape is
quite variable. The size of fulvic acids
(FAs) are smaller than humic acids (HAs),
with molecular weights which range from
approximately 1,000 to 10,000. Fulvic acids
(FAs) have an oxygen content twice that of
humic acids (HAs). They have many carboxyl
(-COOH) and hydroxyl (-COH) groups, thus
fulvic acids (Fas) are much more chemically
reactive. The exchange capacity of fulvic
acids (FAs) is more than double that of
humic acids (HAs). This high exchange
capacity is due to the total number of
carboxyl (-COOH) groups present. The number
of carboxyl groups present in fulvic acids
(FAs) ranges from 520 to 1120 cmol (H+)/kg.
Fulvic acids collected from many different
sources and analyzed, show no evidence of
methoxy (-CH3) groups, they are low in
phenols, and are less aromatic compared to
humic acids from the same sources.
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Because of the relatively small size of
fulvic acids (FA) molecules they can readily
enter plant roots, stems, and leaves. As
they enter these plant parts they carry
trace minerals from plant surfaces into
plant tissues. Fulvic acid (FAs) are key
ingredients in high quality foliar
fertilizers. Foliar spray applications
containing fulvic acid (FA) mineral
chelates, at specific plant growth stages,
can be used as a primary production
technique for maximizing the plants
productive capacity. Once applied to plant
foliage fulvic acids (FAs) transport trace
minerals directly to metabolic sites in the
plant cells. Fulvic acids (FAs) are the most
effective carbon containing chelating
compounds known. They are plant compatible,
thus non-toxic, when applied at relatively
low concentrations.
HUMATES - Humates are metal (mineral) salts
of humic (HAs) or fulvic acids (FAs). Within
any humic substance there are a large number
of complex humate molecules. The formation
of a humate is based on the ability of the
carboxyl (-COOH) and hydroxyl (-OH) groups
(on the outside of the polymers) to
dissociate (expel) the hydrogen ion. Once
the hydrogen ions dissociated a negatively
charged anion (-COO- or -CO-) results. Two
of these anions can bind to positive metal
cations, such as iron (Fe++), copper (Cu++),
zinc (Zn++), calcium (Ca++), manganese
(Mn++), and magnesium (Mg++). The simplified
reaction (-COO- + Fe++ >> -COOFe+ + H)
proceeds to bind two anions, frequently a
-COOH and a -COH group. The humate
composition of any one humic substance is
specific for that substance. Thus there
exists a large variability in the molecular
composition of different humic substances.
Humates from different mineral deposits
would be expected to have their own unique
features.
HUMIC SUBSTANCES AND THEIR INFLUENCE ON SOIL
FERTILITY
Humic substances are a good source of energy
for beneficial soil organisms. Humic
substances and non-humic (organic) compounds
provides the energy and many of the mineral
requirements for soil microorganisms and
soil animals. Beneficial soil organisms lack
the photo synthetic apparatus to capture
energy from the sun thus must survive on
residual carbon containing substances on or
in the soil. Energy stored within the carbon
bonds function to provide energy for various
metabolic reactions within these organisms.
Beneficial soil organisms (algae, yeast,
bacteria, fungi, nematodes, mycorrhizae, and
small animals) perform many beneficial
functions which influence soil fertility and
plant health. For example the bacteria
release organic acids which aid in the
solubilization of mineral elements bound in
soil. Bacteria also release complex
polysacharides (sugar based compounds) that
help create soil crumbs (aggregates). Soil
crumbs give soil a desirable structure.
Other beneficial soil microorganisms such as
the Actinomyces release antibiotics into the
soil. These antibiotics are taken up by the
plant to protect it against pests.
Antibiotics also function to create
desirable ecological balances of soil
organisms on the root surface (rhizoplane)
and in soil near the root (rhizosphere).
Fungi also perform many beneficial functions
in soils. For example, micorrhizae aid plant
roots in the uptake of water and trace
elements. Other fungi decompose crop
residues and vegetative matter releasing
bound nutrients for other organisms. Many of
the organic compounds released by fungi aid
in forming humus and soil crumbs. Beneficial
soil animals create tunnel-like channels in
the soil. The channels allow the soil to
breath, and exchange gases with the
atmosphere. Soil animals also aid in the
formation of humus, and help balance the
concentration of soil microorganisms. A
healthy fertile soil must contain sufficient
carbon containing compounds to sustain the
billions of microscopic life forms required
for a fertile and a healthy plant. A living
soil is a fertile healthy soil.
Humus functions to improve the soil’s water
holding capacity. The most important
function of humic substances within the soil
is their ability to hold water. From a
quantitative standpoint water is the most
important substance derived by plants from
the soil. Humic substances help create a
desirable soil structure that facilitates
water infiltration and helps hold water
within the root zone. Because of their large
surface area and internal electrical
charges, humic substances function as water
sponges. These sponge like substances have
the ability to hold seven times their volume
in water, a greater water holding capacity
than soil clays. Water stored within the
top-soil, when needed, provides a carrier
medium for nutrients required by soil
organisms and plant roots.
Available water is without doubt the most
important component of a fertile soil. Soils
which contain high concentrations of humic
substances hold water for crop use during
periods of drought. This is why growers who
apply humate-based fertilizers and integrate
production practices which preserve humic
substances, can frequently harvest a crop
during periods of dry weather.
Humic substances are key components of a
friable (loose) soil structure. Various
carbon containing humic substances are key
components of soil crumbs (aggregates).
Complex carbohydrates synthesized by
bacteria and humic substances function
together with clay and silt to form soil
aggregate. As the humic substances become
intimately associated with the mineral
fraction of the soil, colloidal complexes of
humus-clay and humus-silt aggregates are
formed. These aggregates are formed by
electrical processes which increase the
cohesive forces that cause very fine soil
particles and clay components to attract
each other. Once formed these aggregates
help create a desirable crumb structure in
the top soil, making it more friable. Soils
with good crumb structure have improved
tilth, and more porous openings (open
spaces). These pores allow for gaseous
interchange with the atmosphere, and for
greater water infiltration.
The mean residence times of these
organo-mineral complex aggregates varies
with different humic substances. The mean
residence time of humic substances within
these aggregates, based on radiocarbon
dating, using extracts from non-disturbed
soil, is as follows: humin, 1140 years;
humic acid, 1235 years; and fulvic acid, 870
years. Man has shortened the residence time
of humic substances by excessive fertilizing
and by using tilling practices that cause
excessive weathering of soils. Soils abused
by applications of anhydrous ammonia and by
other destructive practices (those which
destroy humic substances) can shorten
residence times by several hundred years.
The turnover time of organic carbon added
each year from plant and animal residues
averages approximately 30 years, under ideal
conditions. In order to retain humic
substances within the soil growers need to
implement production practices which prevent
their decomposition. Growers need to develop
practices which retain the residence time of
humic substances. It is essential to avoid
destructive fertilization practices, rotate
crops, minimize pesticides usage, deep
plowing, and mix crop residues in the top
soil by using minimum tillage practices.
Soils which contain adequate humic
substances have improved tilth (work
ability) and are thus more efficiently
maintained for crop production.
Degradation or inactivation of toxic
substances is mediated by humic substances.
Soil humic substances function to either
stabilize or assist in the degradation of
toxic substances such as: nicotine,
aflatoxin, antibiotics, phenols, and most
organic pesticides. In the microbial
degradation process not all of the carbon
contained within these toxins is released as
CO2. A portion of these toxic molecules,
primarily the aromatic ring compounds are
stabilized and integrated within the complex
polymers of humic substances. Humic
substances have electrically charged sites
on their surfaces which function to attract
and inactivate pesticides and other toxic
substances. For this reason the
Environmental Protection Agency recommends
the use of humates for clean up of toxic
waste sites. Many bioremediation companies
apply humate based compounds to toxic waste
sites as a part of their clean up program.
Growers interested in cleaning up their
soils (destroying various toxic pesticides)
can accelerate the degradation of poisons
(toxins) by applying humic substances.
Growers who farm soils low in humus need to
include the purchase of humic substances in
their fertilizer budget. The cost of humic
substances can be more than offset by
reduced costs of other fertilizer
ingredients.
Humic substances buffer (neutralize) the
soil pH and liberate carbon dioxide. Humic
substances function to buffer the hydrogen
ion (pH) concentration of the soil. Repeated
field studies have provided experimental
evidence that the addition of humic
substances to soils helps to neutralize the
pH of those soils. Both acidic and alkaline
soils are neutralized. Once the soil is
neutralized, then many trace elements
formerly bound in the soil and unavailable
to plant roots, because of alkaline or
acidic conditions, become available to the
plant roots. Humic substances also liberate
carbon dioxide (CO2) from calcium carbonates
present within the soil. The released CO2
may be taken up by the plant or it may form
carbonic acids. The carbonic acids act on
soil minerals to release plant nutrients.
Soil enzymes are stabilized and inactivated
by humic substances. Soil enzymes (complex
proteins) are stabilized by humic substances
within the soil by covalent bonding.
Stabilization renders these enzymes less
subject to microbial degradation. Once
stabilized and bound to the humic substances
enzyme activity is greatly reduced or ceases
to function. However many of these bonds are
relatively weak. During periods of pH change
within the soil, these enzymes can be
released. When some components of humic
substance react with soil enzymes they are
more tightly bound. For example,
phenolic-enzyme complexes are frequently
attached to clays, further stabilizing the
enzymes. These enzyme stabilization
processes help to restrict the activity of
potential plant pathogens. As the potential
plant pathogen release enzymes designed to
break down the plant’s defenses, the
pathogens enzymes become bound to humic
substances. As a result the pathogens are
unable to invade potential host plants.
Soil temperatures and water evaporation rate
are stabilized by humic substances. Humic
substances function to help stabilize soil
temperatures and slow the rate of water
evaporation. The insulating properties of
humic substances help maintain a more
uniform soil temperature, especially during
periods of rapid climate changes, such as
cold spell or heat waves. Because water is
bound within the humic substances and humic
substances reduce temperature fluctuations,
soil moisture is less likely to be released
into the atmosphere.
The electrical features of humic substances
influence known chemical reactions. Both
groups of complex organic acids, humic acids
(HAs) and fulvic acids (FAs) have been
proven to be involved in three specific
chemical reactions. These reactions are
commonly termed: (1) electrostatic
(columbic) attraction, (2) complex formation
or chelation, and (3) water bridging.
Electrostatic attraction of trace minerals
reduces leaching into subsoil. Electrostatic
attraction of metal cations to anionic sites
on the humic substance keeps these ions from
leaching into the subsoil. The metal cation
is loosely attached, thus can be released
when attracted to another stronger
electrical charge. The cation is readily
available in the soil environment for
transport into the plant roots or exchanged
for another metal cation
Electrically charged sites on humic
substances function to dissolve and bind
trace minerals. When a complex reaction with
metal cations occurs on the humic substance
surface it is termed chelation. Two
negatively charged sites on the humic
substance attract metal cations with two
negative charges. As a result the cation
binds itself to more than one charged
anionic site. By forming organo-metal
chelates, these organic acids bring about
the dissolution of primary and secondary
minerals within the soil. These minerals
then become available for uptake by plant
roots. The greater the affinity of the metal
cation for humic acid (HA) or fulvic acid
(FA), the easier the dissolution of the
cation from various mineral surfaces. Both
the acidic effects and the chelation effects
appear to be involved in dissolution of
minerals and binding processes. Evidence for
the dissolution of minerals can be supported
by x-ray diffraction and infrared analysis.
Chelation of plant nutrients such as iron
(Fe), copper (Cu), zinc (Zn), magnesium
(Mg), manganese (Mn), and calcium (Ca)
reduces their toxicity as cations, prevents
their leaching, and increases their uptake
rate by plant roots.
The chelation exchange reaction involves a
transition element. The release of these
trace minerals into the plant is quite
different from the classical cation exchange
system. The cation with a plus two charge,
present in the chelate, cannot be replaced
by a singly charged cation such as H+, K+ or
Na+. Cations with one positive charge are
unable to replace a metal ion, such as Cu++,
with two positive charges. The chelated
metal ion can be exchanged by another
transitional ion that has two positive
charges. The chelates provide the carrier
mechanism by which depleted nutrient
elements are replenished at the root
surface. The chelation process also
increases the mass flow of micro nutrient
mineral elements of the root. The chelation
of heavy toxic metallic elements present
within the soil is also influenced by humic
substances present. When toxic heavy metals
such as mercury (Hg), lead (Pb), and cadmium
(Cd) are chelated these organo-metal
complexes become less available for plant
uptake. Detailed studies of chelation of
heavy metals in industrial sludge has
illustrated the value of humic substances in
preventing uptake of these toxic metals.
Keep in mind that free metal cations such as
Fe+2, Cu+2, and Zu+2 are incompatible with
plant cells. Direct applications of metallic
salts, such as iron sulfate, copper sulfate,
and zinc sulfate, to correct trace element
deficiencies, can cause serious problems
when the soils lack sufficient humic
substances for buffering. Trace minerals
should be applied in an organic chelate,
preferably by humic acids (HAs) and fulvic
acids (FAs). Many scientific studies have
shown that humic substances [humic acids
(HAs) fulvic acids (FAs)] present in the
root zone reduce the toxicity of metal
cations.
Water bridging is an important function of
humic and fulvic acids. Water bridging by
humic substances involves the attraction of
a water molecule followed by the attraction
of a mineral element cation (Simply
illustrated by (-COO - H2O -Fe+) at an
anionic site on the humic (HA) or fulvic
acid (FA) polymers. The water holding
capacity of humic substances and their
ability to bind trace mineral elements
function together in water bridging. Water
bridging is believed to improve the mobility
of nutrient ions through the soil solution
to the root. These mechanisms also help
reduce leaching of plant nutrients into the
subsoil. Recent experiments indicate that
water bridging may be more common in humic
substances than originally believed.
Humic substances aid in the decomposition of
soil minerals by forming metal-organic-clay
complexes, a process termed soil genesis.
Soil formation (soil genesis) involves a
complexing of transition mineral elements,
such as copper (Cu), zinc (Zn), iron (Fe),
and manganese (Mn) from soil minerals with
humic acids (HAs), fulvic acids (FAs) and
clays. This complexing process inhibits
crystallization of these mineral elements.
The complexing process is in part controlled
by the acidity of these weak acids and the
chelating ability of humic substances. In
the absence of humic substances trace
minerals elements are converted to insoluble
precipitates such as metal carbonates,
oxides, sulfides, and hydroxides. Thus the
presence of humic acids (HAs) and fulvic
acids (FAs) within soil inhibit the
development of new soil minerals. For
example, crystallization of iron to form
iron oxides is inhibited by the presence of
humic acids (HAs) and fulvic acids (FAs).
Soils deficient in humic substances may
contain adequate iron, however the iron
present is frequently bound in forms which
render it unavailable to plant roots. As the
concentration of fulvic acids (FAs)
increases within a soil. Transition metal
crystallization is first delayed and then
inhibited at high fulvic acid (FA)
concentrations. Cations of these transition
metals (e.g. Cu++, Zn++ and Fe++) are held
in large humic polymers by chelation, for
future release to soil organisms on plant
roots. These physical and chemical processes
prevent leaching of plant nutrients into the
subsoil.
Stored energy and trace mineral content of
humic substances helps sustain soil
organisms involved in transmutation. The
presence of humic substances within saline
soils (those soils which contain high salt
concentrations, e.g. sodium chloride) aid in
the transmutation of the sodium ions. The
transmutation reactions, a biological
process that occurs within living organisms,
result in the combining of sodium with a
second element, such as oxygen, to form a
new element. Although the theory of
transmutation has met considerable
opposition by some traditional physicists
and chemists, biologist have recorded
convincing data to prove that transmutation
occurs in living organisms. Application of
humins, humic acids, and fulvic acids to
saline soils, in combination with specific
soil organisms, results in a reduction in
the concentration of sodium salts (e.g.
NaCl). The reduction is not correlated with
a leaching of the salt, rather with an
increase in concentration of further
elements. The addition of humic substances
to soils containing excessive salts can help
reduce the concentration of those salts. By
reducing the salt content of a soil its
fertility and health can be “brought back”
to provide a more desirable environment for
plant root growth.
HUMIC SUBSTANCES AND THEIR INFLUENCE ON
PLANT GROWTH AND DEVELOPMENT
Plant growth is influenced indirectly and
directly by humic substances. Positive
correlations between the humus content of
the soil. Plant yields and product quality
have been published in many different
scientific journals. Indirect effects,
previously discussed, are those factors
which provide energy for the beneficial
organisms within the soil, influence the
soil’s water holding capacity, influence the
soil’s structure, release of plant nutrients
from soil minerals, increased availability
of trace minerals, and in general improved
soil fertility. Direct effects include those
changes in plant metabolism that occur
following the uptake of organic
macromolecules, such as humic acids, fulvic
acids. Once these compounds enter plant
cells several biochemical changes occur in
membranes and various cytoplasmic components
of plant cells. Some of the biochemical
improvements in plant metabolism, as
influenced by humic substances, are
summarized in Figure 2.
Uptake of major plant nutrients is mediated
by humic substances. One stimulative effect
of humic substances on plant growth is
enhanced uptake of major plant nutrients:
nitrogen (N), phosphorus (P), and potassium
(K). When adequate humic substances are
present within the soil the requirement for
N-P-K fertilizer applications is reduced. As
the level of humic substances in soils
become depleted the misleading demand for
higher concentrations of N-P-K results. Many
growers have over the past several years
reported increasing demands for soluble acid
fertilizers in order to maintain crop
yields. Such observations indicate something
is wrong within the soil. Increased leaching
of nitrate fertilizer ingredients into the
ground water is also a warning of problems
to come. These trends reflect losses in soil
humic substances. Growers could reduce their
fertilizer requirements and retain the
fertilizer ingredients within the plants
rooting zone by the application of humate
based fertilizers. The application of either
dry or liquid humic substances to soils
dramatically increases fertilizer
efficiency. Other researchers have reported
increased uptake of calcium (Ca), and
Magnesium (Mg) when plants are irrigated
with liquid suspensions of humic acids (HAs)
or fulvic acids (FAs). Another key
mechanism, which maximizes fertilizer
efficiency and relates to a function of
humic substances, is a reduction in the
toxicity and leaching of nitrogen compounds
into subsoil water. Humic substances hold
these major plant nutrients in a molecular
form which reduces their solubility in
water. These binding processes reduce
leaching nitrogen into the subsoil and help
prevent volatilization into the atmosphere.
The absorption of humic substances into
seeds has a positive influence on seed
germination and seedling development. The
application of humic (HA) or fulvic acids
(FA) to seeds will increase the seed
germination; resulting in higher seed
germination rates. Application rates of
humic acids (HAs) or fulvic acids (FAs),
required for improved seed germination,
range from 20 to 100 mg/liter of seed. In
order for improved germination to occur the
humic substances must be present within the
cells of seeds. As the humic substances
enter the seed cells, respiration rate
increases, and cell division processes are
accelerated. These same respiratory
processes enhance root meristem development
and activate other growing points within the
seedlings. Humic substances have been
demonstrated to enhance mitotic activity
during cell division under carefully
controlled experiments. Placement of these
humic substances on seed (seed treatment) or
within the seed furrow will significantly
improve seed germination and seedling
development. Excessive concentrations of
humic acids (HAs) and/or fulvic acids (FAs)
can inhibit seed germination and at high
concentrations can kill young seedlings.
Therefore follow recommended rates when
applying humic substances.
Humic substances have a very pronounced
influence on the growth of plant roots. When
humic acids (HAs) and/or fulvic acids (FAs)
are applied to soil, enhancement of root
initiation and increased root growth are
observed. Thus the common observation that
humic acids (HAs) and fulvic acids (FAs) are
root simulators. In most experimental
studies plant root growth is stimulated to a
greater extent compared to stimulation of
aboveground plant parts. Carefully designed
experiments have been conducted under
controlled conditions to measure plant
responses. For example, replicate treatments
of plants grown within the greenhouse, with
and without humic acids and fulvic acids has
illustrated how humic substances influence
root growth. In treated root weights
averaged from 20 to 50% heavier compared to
the weights of non-treated roots. The type
of humic substances applied had a
significant influence on the percent of
increase. Not all humic substances contain a
desirable molecular mixture of humins, humic
acids (HAs) and fulvic acids (FAs) capable
of rapid stimulation root growth. Some humic
substances, because of their large molecular
sizes, failed to stimulate plant root
development. Root stimulation occurs when
the smaller molecular components within
fulvic acids (FA) occur at a concentration
which ranges from 10 to 100 mg/liter of
solution. Growth is further stimulated when
fulvic acids (FAs) are used in combination
with HUMIC acids (HAs) and other required
plant nutrients. Humic substances improve
plant nutrition, however they are not
complete nutrients by themselves.
Excessively high concentrations of humic
substances can result in a reduction in root
weight. For optimum plant growth humic acids
(HAs) and fulvic acids (FAs) should be
applied at relatively low concentrations.
Application of HUMIC substances within a
fairly wide range of concentrations are
highly beneficial to plant root development.
Humic acids (HAs) and fulvic acids (FAs) are
excellent foliar fertilizer carriers and
activators. Application of humic acids (HAs)
or fulvic acids (FAs) in combination with
trace elements and other plant nutrients, as
foliar sprays, can improve the growth of
plant foliage, roots, and fruits. By
increasing plant growth processes within the
leaves an increase in carbohydrates content
of leaves and stems occurs. These
carbohydrates are then transported down the
stems into the roots where they are in part
released from the root to provide nutrients
for various soil microorganisms on the
rhizoplane and in the rhizosphere. The
microorganisms then release acids and other
organic compounds which increase the
availability of plant nutrients. Other
microorganisms release “hormone-like”
compounds which are taken up by plant roots.
The required concentration of humic acids
(HAs) and/or fulvic acids (FAs) within the
foliar spray should be relatively low,
generally less than 50 mg of concentrated
dry humic substance per liter of water.
Foliar fertilizers containing humic acids
(HAs) and fulvic acids (FAs) on combination
with nitrogen, potassium, phosphorus and
various trace minerals have been
demonstrated to be from 100 to 500% more
efficient compared to applications of
similar fertilizers to the soil. Foliar
fertilizers are also more economical because
smaller quantities of fertilizer are
required to obtain significant plant
response. Plant nutrients within foliar
fertilizers are rapidly absorbed by the
plant leaves. Within 8 hours after
applications of humic substances are
applied, changes in many different metabolic
processes are detected. Enhanced
carbohydrates production can be detected
within 24 to 48 hours after foliar feeding
by use of a refractometer. Enhanced
carbohydrate production can either result in
improved product quality or increased
yields.
Young plant roots, and growing plants are
more responsive to applications of humic
substances. Actively growing plant tissues
are the mist responsive to applications of
humic substances. Younger tissues have
active transport mechanisms that move the
required nutrients to sites of metabolic
activity. For example, foliar applications
of humic substances to young actively
growing leaves results in a greater increase
in plant growth when compared to foliar
applications to older plant leaves. Actively
growing plant parts involved in cell
divisions and other growth processes,
readily integrate various trace minerals and
growth regulating compounds into on-going
metabolic processes. In contrast older plant
parts in which metabolic processes have
slowed are unable to efficiently utilize
added humic substances and associated
nutrients. The concentrations of dry humic
acids (HAs) within the spray solution should
range from 5 to 100 mg per liter of water
for optimum response. Differences in the
active ingredients of a specific substances
may require changing these concentrations.
At higher concentrations, above 100 mg of
dry humic acids (HA) per liter, plant,
shoot, and even root growth may be
inhibited, depending on the substances under
test. Plants respond more slowly to soil
applications of humic substances because a
large percentage of the humic substances is
retained within the roots during plant
growth. In most plants less than 30% of the
humic substances present within the roots
are translocated up the stems into the plant
leaves. Foliar applications of relatively
small molecular units of humic substances
containing trace minerals (on actively
growing plants) can be timed to meet the
needs of specific plant growth requirements.
Applications can be timed to activate
vegetative growth, flowering, fruit set, or
filling and ripening of fruits.
Side dress applications of commercial liquid
humic acids (HAs) and fulvic acids (FAs) to
soils during crop production results in
direct root uptake. As noted above when
humic substances are taken up by plant roots
these compounds become concentrated within
the roots. Uptake of smaller molecular
components of humic substances is both
passive and metabolically active. The uptake
of high molecular weight humic acids (HAs)
by roots is primarily passive; while the
uptake of smaller fulvic acids (FAs)
polymers is primarily metabolic. After humic
acids (HAs) and fulvic acids (FAs) reach a
concentration in the root, then a fraction
(from 5-30 %) of the total concentration is
transported into the shoots and leaves.
Radioactive carbon studies indicate that the
greatest concentration of humic substances
accumulates in plant cell walls and cellular
organelles such as the mitochondria and
ribosomes. Other similar experiments using
radioactive carbon labeled humic acids (HAs)
and fulvic acids (FAs) indicates that low
molecular weight fulvic acids (FAs) are much
more active compared to high molecular
weight humic acids (HAs). However some
metabolic reactions may require low
concentrations of humic acids (HAs) in
combination with fulvic acids (FAS). Root
growth is primarily stimulated by the
molecular components of humic acids (HAs)
and fulvic acids (FAS).
Humic acids (HAs) and Fulvic acids (FAS)
have direct effects on plant cell membranes.
HUMIC acids (HAs) increase the permeability,
ease by which mineral elements move back and
forth through the cell membranes, resulting
in an increased transport of various mineral
nutrients to sites of metabolic need. Humic
substances influence both hydrophilic
(having water affinity) and hydrophobic
(lacking water affinity) sites on the
membranes surfaces. In addition, many
scientists believe that the phospholipid
components of the membranes are electrically
altered by humic substances. As a result of
these electrical changes, the membrane
surface becomes more active in the transport
of trace minerals from outside the plant
cell into the cell cytoplasm.
Energy metabolism is accelerated and the
chlorophyll content of plant leaves is
enhanced by the presence of humic
substances. When Humic Acids (HAs) and
fulvic acids (FAS) are applied to plant
leaves the chlorophyll content of those
leaves increases. As the chlorophyll
concentration increases there is a
correlated increase in the uptake of oxygen.
Chlorophyll development within plant leaves
is more pronounced when fulvic acids (FAS)
are present in the foliar fertilizer.
Organic acids [humic acids (HAs) and fulvic
acids (FAS) also increase the concentration
of messenger ribonucleic acids (m-RNA) in
plant cells. Messenger RNA is essential for
many biochemical processes within cells.
Activation of several biochemical processes
results in an increase in enzyme synthesis
and an increase in the protein contents of
the leaves. During these metabolic changes
an increase in the concentration of several
important enzymes is detected. Some of the
enzymes which are reported to increase are:
catalases, peroxidases, diphenoloxidase,
polyphenoloxidases, and invertase. These
enzymes activate the formation of both
carrier and structural proteins.
Some molecular components of humic
substances act to regulate plant growth
hormones. Both humic acids (HAs) and fulvic
acids (FAs) inhibit the enzyme, indole
acetic acid oxidase (IAA-oxidase), there by
hindering IAA destruction. The plant growth
regulator, indole acetic acid (IAA) performs
many important functions within growing
plant parts. When IAA is protected from IAA
degrading enzymes the IAA continues to
stimulate growth processes. Unfractionated
humic acids (HAs) are the most effective in
regulating plant growth hormones. Humic
substances also influence other enzymes
involved in growth regulation. When the
activity of growth regulators is maintained
within plant tissues, plant metabolism
remains functional and normal growth
processes continue to occur.
Humic substances increase production of high
energy adenosine triphosphate (ATP) within
plant cells. As various metabolic systems
are activated by humic substances an
increase in the production of high energy
phosphate bonds (ATP) occurs. The high
energy phosphate bonds of ATP function as a
major driving energy for many different
metabolic reactions.
Humic substances provide many free radicals
to plant cells. Free radicals are “active
sites” on the polymers which function as
electron donors. Free radicals assist in
exerting positive effects on seed
germination, root initiation and plant
growth in general. Free radicals contain one
or more unpaired electrons, are highly
reactive, short lived, and capable of
participating in many different reactions.
The free radical content of humic substances
is related to the humification state of the
humic substance. The greater the
humification (low H:C ratios) the darker the
color of the humus. Thus humic acids (HAs)
contain a higher free radical content
compared to fulvic acids (FAS), which have a
high H:C ratio. The relatively low free
radical content of fulvic acids (FAS),
associated with high H:C ratios, is
indicative of a low degree of chemical
condensation for these substances. Humic
acids (HAs) contain two types of free
radicals. The first class is a permanent,
stable type which persists for longer
periods. The second class is a transitional
paramagnetic type which is transitory. Each
free radical type has a specific function
(e.g. catalyst, photo sensitizer, and
activators) in various metabolic processes
within living cells.
SOURCES OF HUMIC SUBSTANCES AND THEIR VALUE
AS FERTILIZER INGREDIENTS
Humic substances commonly occur within
soils, waters, peat, and in carbon
containing minerals such as brown coals, low
grade lignites, and leonardites. Most all
soils and waters on the earth surface
contain some humic substances in the form of
humin, humic acids (HAs), or fulvic acids
(FAS). However the concentration of humic
substances in agricultural soils has reached
seriously low levels. In general soils
contain a higher concentration of humin and
humic acids (HAs). In contrast, since fulvic
acid (FA) is water soluble it occurs at
relatively high concentrations in both soils
and water. Soil humic substances consist of
a higher percentage of ring compounds
(aromatic) compared to humic substances from
water. Fertilizer grade humic substances can
be obtained from carbon containing mineral
deposits throughout many parts of the world.
Within the United States there are several
mines and seams of carbon containing mineral
deposits suitable for obtaining good
agricultural grade humic substances.
Humic substances can form naturally within
soils properly managed. Certain production
practices can help build the humus content
of soils. Practices such as crop rotation,
using balanced fertilization programs,
planting legumes, plowing under green
manures, returning organic matter to the
land, applications of compost, and using
minimum tillage practices can all help build
humus. Any production practices which damage
the activities of living components of the
soil should be avoided. Protect the
beneficial organisms responsible for forming
humus, and they will perform their jobs.
Humus building practices are slow, time
consuming, and may be costly, however they
pay large dividends over time. In order to
rapidly return many damaged soils to their
former productive capacity growers should
consider additional alternatives. An
analysis of this situation indicates that
the most rapid and practical solution to
improving soil fertility is the addition of
humates (mined humic substances) directly to
the soil or as foliar fertilizers. On most
soils the applications of humate based
fertilizers is more important than applying
traditional N-P-K fertilizers. Humic
substances will maximize the efficient use
of residual plant nutrients, reduce
fertilizer costs, and help release those
plant nutrients presently bound in minerals
and salts.
Naturally occurring humic substances from
low grade lignites and leonardites (natures
soil conditioners), are superior fertilizer
ingredients. The best source of humic
substances for fertilizer use is from
leonardites. Leonardite is defined as a
highly oxidized low grade lignite that
contains a relatively high concentration of
the smaller molecular units (fulvic acids).
The smaller humic acids (HA) and fulvic acid
(FA) molecules have higher fertilizer value
and are readily taken into the plant along
with trace minerals. The quality and value
of any one mined humate or humic acid
product depends on many different factors. A
good humic material can be destroyed by
improper mining or processing. Thus not all
commercially marketed humic substances are
equal in quality. It is very difficult for
individuals purchasing a humate based
fertilizer to tell the difference between a
high quality humic substance and a low
quality humic material, without laboratory
tests. The real test of any humic product is
in the field. Growers interested in
improving soil fertility and plant health
need to set up field tests, with an open
mind. Many growers have tried several
different commercial humic substance before
discovering one that improves crop yields
and product quality on their soils. In
setting up test plots it is best to
establish side-by-side comparisons in the
field with a uniform soil type. The whole
field should be fertilized as usual and the
second half treated with a dry humic
substance before planting. In addition
liquified humic substance should be applied
to the soil and to the foliage as spray
during the growing season. In selecting a
specific commercial humate product the major
concern relates to product quality.
Determine if the humate is a blend of humic
acids and fulvic acids or is it primarily
humic acids. Avoid purchasing pure humic
acids. Secondly, does the marketed product
have consistency between different batches.
An erratically performing product is of
minimal value. Another important question
is, how rapidly does the product perform in
terms of its ability to improve plant
growth? One of the best approaches is to ask
around and find out which company has
quality control procedures in their mining
and industrial processing operations.
Established companies with experience of
working with humates and have a good track
record generally market superior
humate-based fertilizers.
Quality of humic substances extracted from
composts are influenced by the composting
ingredients and techniques. Compost starting
materials that contain large molecular
compounds such as lignins, paraffinic
macromolecules, suberins, melanins,
cellulose (wood products) and various
polyphenols have superior values. In
addition to these more complex compost
ingredients a blend of compounds containing
smaller molecules, such as animal wastes or
sludge should also be added to the compost.
The length of the composting period, how the
compost is turned and watered also
influences the quality of compost. A
superior compost can be prepared by adding
dry Leonardite in with the plant and animal
wastes. The added Leonardite creates a more
complete balanced of trace mineral elements
required by the composting microorganisms.
With time the microorganisms and small
animals present can synthesize complex humic
substances. A large percentage of the
currently available plant and animal
residues have originated from heavily mined
agricultural soils. Many of the by-products
of the food industry lack important minerals
and vitamins. This fact should be evident
from observed vitamin and mineral
deficiencies, observed in man and animals.
The vitamin and mineral supplement industry
is based on the fact that marketed foods and
feeds lack certain nutrient requirements. By
applying a complete humate based fertilizer
or a more complete compost, soil fertility
and plant health can be restored.
New standards are needed to monitor the
quality of humate based fertilizers
currently marketed. The consumer needs
protection from inferior products. There are
many “humic acid type” products currently
marketed in he United States. Some of these
“humic” products have been developed by
industrial chemists, industrial concerns
have made many attempts to manufacture humic
acids using different industrial processes.
As a result several “synthetics” have been
produced, marketed, purchased, and used.
Most of these synthetics have been polymers
of vinyl acetate, maleic acid, polyvinyl
alcohol, hydrolyzed polyacrylonitrile,
carboxymethylcellulose, polyacrilates,
isopropyl acrylamide and poly-quaternary
ammonium compounds. Generally these
synthetic humic molecules have performed
poorly in terms of their ability to improve
soil fertility or plant growth. These
products should not be defined as humate
based fertilizer ingredients since their
performance under field conditions are very
erratic. A chemical analysis of their
molecular features reveals that these
“synthetics” lack many of the properties of
naturally occurring humic substances. They
lack the molecular features which improve
soil fertility and are frequently
incompatible with plant metabolic processes.
Other industrial groups have obtained from
mature, alkali-insoluble lignite-like coals,
treated these materials with degradative and
oxidation processes to produce smaller
alkali soluble “humic” solutions. The
resulting oxidized mixtures from black coals
or lignite coals are termed “regenerated
humic acids” or “ulmins”. These “ulmins”
have characteristics which are similar to
humic acids derived from low grade lignites,
however are quite different chemically, thus
the term “regenerated” is a misnomer. There
is no evidence that these “ulmins” have
desirable fertilizer grade properties.
Hopefully members of the International Humic
Substances Society can propose quality
standards (labeling) for all commercially
marketed humic substances and develop
laboratory procedures capable of monitoring
the quality of listed ingredients. Until
standards can be designed, which are
acceptable to the industry, growers and
gardeners should purchase humate based (dry
and liquid) products that have been
extracted from highly oxidized mined low
grade lignites or leonardites. Humic
substances from such mineral deposits more
closely resemble humic substances normally
found in fertile soils and in healthy
plants.
Application of humate based dry or liquid
fertilizers can improve product quality and
increase production. As outlined above humic
substances are the building blocks of
fertile soils and healthy plants. One
important reason for adding humate based
fertilizers to the soil is that the producer
can again become a steward of the soil. By
developing a more ecologically sound
agricultural productions system it is
possible to reduce soil, water, and air
pollution. In addition, crop yields will
improve and the nutritional value of the
harvested products will significantly
improve in quality. The extent to which
humate based fertilizers improve crop yields
depends on the history of cropping practices
used on each field. Soils severely damaged
by excessive use of acidic fertilizers or
pesticides generally respond slowly the
first year. Generally the first improvements
observed are in product quality. As toxic
soil conditions are remediated (corrected)
and additional humate-based fertilizers are
applied, crop yields and product quality
continue to improve.
A word of caution. Avoid applying excess
fertilizers (of any type) to soils or plant
surfaces. Individuals who apply fertilizers
to soils (e.g. producers, farmers, and
gardeners) should keep in mind that
excessive applications of any fertilizer can
create imbalances and even reduce soil
fertility. The positive impact of humic
substances on plant growth can be reversed
by applying excessively high concentrations
of these fertilizers. Follow recommendations
that have been based on many years of
experience. |
