Watch this science video tutorial from Nurd Rage on how to test if a fertilizer has nitrates rather than urea or ammonia as its nitrogen source.
The idea is quit simple, in a strongly acidic solution the nitrates will behave like nitric acid and dissolve copper metal releasing nitrogen dioxide gas. Looking for this gas is a strong indication for the presence of nitrates.
WARNING: These reactions produce toxic nitrogen dioxide gas, this must be performed outside or in a fume hood.
To perform the test, simply mix some of your fertilizer with water to dissolve the nitrates and then mix it with hydrochloric acid. Then add in some copper metal.
The reaction is very slow to start up unless you heat it. A nerdy way of heating it on the spot without using a heater is to add a small ball of aluminum metal, don't use too much or it will go out of control. Stir the mixture as the aluminum dissolves to distribute the heat evenly.
After the mixture is heated, place a glass container over the mixture to keep the gases in. If nitrogen dioxide is forming the distinctive brown nitrogen dioxide will fill the container.
And that's how you can tell if there are nitrates in your fertilizer.
If you want to test for ammonia (in case you have ammonium nitrate) just mix some fertilizer with half as much sodium hydroxide and add a little water to cover it. If it starts bubbling and releasing ammonia gas then it contains ammonia.
Brought to you by one of WonderHowTo's favorite scientists NurdRage.