Originally Posted by danielt
Can you elaborate a bit on that? What does organic nitrogen mean? AFAIK, the organic form is not accessible to plants as it is a too complex compound, just like organic carbon. It needs to be broken down to more simpler, inorganic, forms like NH3/NH4 before the plant can use that. The fertilizer nitrogen is indeed inorganic. Although plants prefer NH3 and NH4 before NO3.
Organic nitrogen is referring to nitrogen derived from organic sources such as fish waste, uneaten food, decomposing plant matter, etc. High levels of organic nitrogen are usually a sign of poor water quality due to lack of maintenance, etc.