Plants need nitrogen. You’re soaking in it – the air is 78% N2 Trouble is, the kind of nitrogen plants need is reduced (i.e., has more electrons) relative to dinitrogen in the air. In the past, this meant rotating crops – peanuts, for example, promote nitrogen-reducing, or “nitrogen-fixing” bacteria.
We learned some time ago, though, that we could fix our own nitrogen. The Haber-Bosch process can take dinitrogen and dihydrogen and produce significant amounts of ammonia – “fixed” or reduced nitrogen. You can use ammonia as a fertilizer – if you keep it in big tanks like you use for BBQ propane, you can keep liquid ammonia around (it boils well below zero). If you mix ammonia with nitric acid, you can make ammonium nitrate, an easy-to-handle solid:
Problem is, nitrate is a pretty good oxidizer, and you’ve got all that reduced nitrogen around to react with it. Ammonium nitrate is actually a pretty good explosive, and it’s even better when you have some more fuel around – like diesel. Ammonium nitrate/fuel oil, or ANFO, was used by American terrorist Timothy McVeigh on his attack on the Oklahoma City Federal Building.
The fact that fertilizer, which is ubiquitous, contains a potential explosive component, is the subject of much consternation. Tomorrow, a proposed solution.