Yes exactly. I didn't mention that nitrate can be gotten from ammonia or nitrate because those really shouldn't be in a planted tank anyways I said that nitrogen is more important than iron, but that's just because more of it is used. Really, nitrogen, iron, carbon, potassium and a few other elements are all "essential" in that they play a critical part in plant functioning at some point or another. What luke said isn't true obviously, but what he probably meant was iron is one of the most important to supplement, which is true. Usually enough nitrogen is produced for most people to not have to worry about supplementation.