Ammonium Nitrate _is_ fertiliser. You make a better bomb if you add some kerosene. At least, so I've heard. ANFO.
AFAIK this is the only time a terrorist organisation (anyone know which one? ) contributed something useful to the body of knowledge used by civilisation.
Mining used to employ high explosive (Dynamite, TNT, etc.) which is expensive and non-trivial to store and in some cases toxic to handle. Open-cast mining has now adopted ANFO - cheaper, non-toxic, and manufactured down the hole where you want the explosion. Nitrate fertilizer first, then add fuel oil, then top with a detonator.
BTW Ammonium Nitrate is also an explosive on its own. You do have to hit it very hard before it goes bang, but if you manage to do so, watch out. One of the largest non-nuclear explosions ever was in the Netherlands when the roof of a warehouse full of Ammonium Nitrate leaked, and the entire contents set solid. Someone had the bad idea of loosening it up with a few sticks of dynamite. He did not survive the several-kiloton non-nuclear explosion which resulted.