I may be wrong, but I always thought that the N in most of the N-P-K
formulations, like 10-10-10, triple-13, etc. was in the form of
NH4NO3. Can't say that I've really sat down and read the label, but
the little 'prills' in 10-10-10 look an awful lot like the little
round prills in my bag of pure A.n.