Nitrogen (N) is an
essential, macronutrient for the growth of almost all
plant life. It makes up around 80% of the atmosphere of
the earth but is not available to plants in the gaseous
form. It must be transformed into another molecule
before it can be used by plants.
The most common form of
nitrogen used by most plants is the nitrate or
NO3- molecule. A few types of
plants prefer their nitrogen in the ammonium form which
has a chemical formula of NH4+. Bacteria located in the soil
are able to transform ammonium into the nitrate form.
Nitrogen tends to be very
water soluble. Therefore, it often leaches through the
soil especially in sandy types and is lost to the roots
of plants. Unlike other nutrients, it does not build up
in the soil so it needs to be replenished each growing
Fertilizers - Every bag of
fertilizer must contain 3 numbers that represent the
percentages of the following nutrients: Nitrogen -
Potassium. So, the first number on a bag
of 18-12-10 fertilizer shows that it contains 18%
To take the nitrogen from
the air and turn it into nitrates or ammonium requires a
large input of electricity. That makes nitrogen the most
expensive of the three macronutrients in a bag of
fertilizer. BTW - Ever notice that things seem to "green
up" after a thunder storm? Well, part of that is due to
nitrates being formed by the electrical exchange that
occurs in lightning.
Since nitrogen is a
universally necessary nutrient for plant growth, it is
available in a large number of types of
Some of these are useful to the home landscape owner
while others are more pertinent to large scale
agricultural or horticultural applications.
This is the form that is most commonly and quickly
used by plants. It is available to plant roots in
almost all types of situations in the soil and does
not need to be converted to any other form. This
form of nitrogen does not become attached to soil
particles and moves freely in the soil water. It
works best when applied frequently but in low levels
to avoid the leaching of excess amounts.
Fertilizers - All the typical bags of fertilizer
that you find at the local garden center or
hardware store contain nitrate type nitrogen. As
soon as the granule dissolves in water, it
becomes available to the plants.
Fertilizers - The standard liquid fertilizers
used for container grown plants also contain the
nitrate form of nitrogen.
Fertilizers - There are a number of special
fertilizers that contain the nitrate form but
they would rarely, if ever, be used in the home
landscape. These would include calcium nitrate,
potassium nitrate and sodium nitrate.
This type of fertilizer quickly transforms into
ammonium once it is placed in the soil. Ammonium
will attach itself to soil particles and is,
therefore, not as readily lost through leaching as
is nitrate. However, before it can be used by
plants, ammonium must be changed into nitrate by
microorganisms in the soil. For this to happen, the
conditions must be right for these organisms to
thrive including adequate heat, moisture and oxygen.
Once the material is changed to nitrate, it is
becomes water soluble and susceptible to leaching.
nitrogen products have an acidifying effect on the
soil. This is valuable for certain "acid-loving"
plants such as
pin oak, heaths, heathers, etc.
Organic Nitrogen: Organic nitrogen is in the form of
protein or other insoluble compounds found in
plant and animal products such as blood meal,
manure and sewage sludge.
In order for the nitrogen to be turned into nitrates
that are then available to plants, these materials
must be broken down by microorganisms in the soil.
The rate at which this takes place depends on soil
temperature, oxygen and moisture levels. Therefore,
organic forms of nitrogen tend to be slow release
and not water soluble until they have been changed