Well, but I don't have any use of all that Nitrogen! At least not until the atmospheric Nitrogen has gone through the process we call Nitrogen Cycle
Nitrogen is all around us! In fact, Nitrogen makes up 78% of the earths atmosphere!
The first step is called Nitrogen fixation, this is were Atmospheric Nitrogen changes to ammonium (NH4+).
This can also happen through lightning strikes... When the Atmospheric Nitrogen splits (by the lightning) in to Nitrogenous Compounds which goes down to the roots of the plants.
Now it is the process called Nitrification, this is were nitrifying bacteria converts Ammonium to Nitrates (NO3)
Now it is time for Nitrification, this is were plants absorb the Nitrogen compounds and make proteins of it.
Then the animals eat the plants to get the protein and utilizes the Nitrogen, and when they poop their waste material contains lots of nitrogen!
After a long time the poop starts to decay and ammonia is released, with goes back to the soil and is again converted to Nitrates. Some of them are used again by plants but the rest gets denitrified and goes back out in the atmosphere.