Fertilizers are not plant food! Although it is common
practice to call them food, this is a misnomer.
Plants produce their own food using water, carbon
dioxide and energy from the sun in the presence of
chlorophyll in a process called
Animals extract the energy trapped in
the vegetative matter by eating it as food. Food implies
a breaking down of complex matter into its component
parts. Plants take the component parts and build them
into complex organic matter. Nutrients in their
environment comprise one of the vital component parts of
Fertilizers help provide these nutrients.
Plant nutrients consist of 17 elements essential to
plant growth. Nitrogen,
considered fertilizer macronutrients because plants
require them in larger quantities for maximum growth.
However, plants also need all of the other 14 elements
in smaller amounts for proper growth. Fortunately, these
minor elements are generally available in typical
By law, all products that claimed to be nutrients for
plant growth i.e. fertilizers, must be labeled with three numbers. These
three numbers give the percentage by weight of nitrogen
(P205) and potash (K2O).
A fertilizer is said to be complete when it contains
some percentage each of
(P) and potassium
(K). Examples of
commonly used complete fertilizers are 12-12-12, 26-16-16,
An incomplete fertilizer will be missing one or
the major components. Examples would be Urea 46-0-0, muriate of potash 0-0-60 or super phosphate 0-33-0.
Cottonseed meal, blood meal, bone meal, hoof and horn
meal, fish emulsion and all manures are examples of
organic fertilizers. Organic fertilizers usually contain
relatively low concentrations of actual nutrients, but
they perform other important functions which the
synthetic formulations do not. These functions include:
increasing organic content of the soil, improving
physical structure of the soil and increasing bacterial
and fungal activity.
Although it is generally agreed that fertilizers come
in three physical forms (liquid, solid and gas), there
are actually only two classes of fertilizers: liquid and
solid. Anhydrous ammonia (NH3) is a gas, but
it is classified as a liquid because it is a liquid
under pressure. The term liquid fertilizer applies to
anhydrous ammonia, aqua ammonia, N solutions and liquid
mixed fertilizers. Liquid N- P- K fertilizers are also
known as fluid fertilizer. They include true solutions
which require no agitation and suspensions or slurry
type mixtures of N, P and K, which require constant
stirring to keep the solids suspended in the solution.
Liquid or fluid fertilizer use has
increased steadily over the last 3 decades, 9%
of the total fertilizer sales consisted of
liquids. Liquid fertilizers account for about 28% of the
Dry fertilizers (solids) still constitute the major
part of the fertilizers sold. About 92%
of the total dry fertilizer is sold as bulk material to
farmers while only 8% in bags for the home consumer. Urea is the most popular
source of dry N fertilizer, accounting for 79% of the
total dry N sold. Ammonium sulfate has risen in
popularity and constitutes around 14% of the dry N
Plant responses to liquid and dry fertilizer are
similar, provided the same amounts of plant nutrients
are applied and the same placement and water are similar. When placed in the soil, dry
fertilizers absorb water and undergo chemical reactions
similar to liquid fertilizer.
Characteristics and Uses
There are several properties of fertilizers and
principles of fertilizer application which users should
become familiar with. One important property of
fertilizers is water solubility. Nearly all nitrogen
fertilizers are completely water soluble. Because of
their high water solubility, granule size and band
placement are generally not important.
Effects of Over-Fertilizing
Fertilizers belong to the chemical category called salts.
Salts have the characteristic of drawing moisture from
their surroundings into the salt. When excessive amounts
of fertilizers (or fresh manures) come into contact with
plant roots, they will pull the moisture from the roots
toward the salt. This collapses the plant cells and
causes rapid dehydration of the plant tissue which is
often called "burn".
Of course another impact of over-fertilization is
that the excess nutrients may be leached or washed away
and into a body of water such as a lake or stream.
There, they may stimulate algae blooms causing a
decrease in the water quality and having a negative
impact on aquatic life.