Ray @ First Rays Orchids ) wrote:
: For some reason, the N-P-K numbers on a fertilizer label are expressed as
: weight percent N, P2O5 and K2O, even though none of them really is in the
: package as those chemical species.

I don't know the justification but it's a fairly common practice. Aqeous N
is often expressed as NO3. I would guess it's a convenience similar to the
reason industrial chemists use molal instead of molar units.

Speaking of chemical species what's the rationale for the preference of
N as ammonia over N as urea?

Dave Sheehy