What are chemical fertilizers, and why do we use them?

The Houston Chronicle by Eric Berger 18 April 2013

What is fertilizer made of?

A commonly manufactured fertilizer is ammonium nitrate, a chemical compound with the symbol NH4NO3. A white crystalline solid at room temperature, nitrogen forms about one-third of this compound. Ammonium nitrate is popular as a fertilizer because it is very soluble in the soil and the nitrate can move deep into the root zone under wet conditions.

Is ammonium nitrate explosive?

Under normal heating conditions no — ammonium nitrate decomposes into two gases, nitrous oxide and water vapor. However, when detonated it can decompose explosively. It is a common ingredient in AFNO, an explosive material used by industry today.

What about anhydrous ammonia?

Anhydrous ammonia — ammonia without water — is an efficient and widely used source of nitrogen fertilizer. It is relatively easy to apply by injection into the soil, and readily available. However, it must be stored under pressure in a liquid state. In gas form it can be set off by water.

So what happened in West?

It’s not entirely clear. It is possible that there was an accident of some kind that led to an explosion of ammonium nitrate, and that in an effort to control that fire, water used set off anhydrous ammonia. That could have led to a chain of explosions. This will all have to be determined in subsequent weeks of investigation. It is likely that this explosion will have a profound impact on federal regulations of chemical fertilizer manufacturing.