Nitrogen can be found in several different forms in the environment.
There is a process in nature which converts nitrogen from one form to
another as different organisms use it. This is called the Nitrogen
Cycle.
Some of the more important forms of nitrogen found in the Nitrogen
Cycle
include:
The first thing to consider with your question is what form of nitrogen
can plants take up. Plants can take up only two forms of nitrogen -
ammonium and nitrate.
Ammonium and nitrate are produced in several different ways. Ammonium
is
manufactured for agricultural and industrial use, made by nitrogen
fixing
bacteria, and is an end product of decomposition. Nitrate is converted
from ammonium by bacteria by a process called nitrification. Nitrate
is
also formed by lightning strikes.
I should mention the difference between ammonia and ammonium is that
ammonium is in solution with water. There is usually a equilibrium
between the two forms that looks something like this:
NH3 + H2O <=> NH4+ +
OH-
You might wonder what difference ammonium and nitrate have on plant
growth. Ammonium is in a reduced form that the plant can use directly
to
form amino acids and other necessary molecules. This means it is
readily
available and causes an increase in vegetative growth. Nitrate, on the
other hand must be reduced by the plant into ammonium before it can be
used. Which fertilizer a farmer or grower will use depends on the crop
being grown and the growing conditions.
For a more information on the nitrogen cycle, including a good diagram,
try this web
site.
Thanks for the question!
Eric J. Biddinger
Grad Student - Department of Horticulture
Penn State University ejb190@psu.edu