You need only nitrogen for explosives, but nitrogen, phosphorus, and potassium for fertilizer. Therefore guano (which contains all three) is overkill for explos

You need only nitrogen for explosives, but nitrogen, phosphorus, and potassium for fertilizer. Therefore guano (which contains all three) is overkill for explosives but great as a fertilizer, while synthetic nitrogen compounds are insufficient as a "complete" fertilizer and have to be supplemented with the two other elements from other sources.