Question
what are the importance of nitrogen compounds in home gardening

Answer
Plants build proteins out of Nitrogen compounds in the soil.  Chlorophyll (C55H70MgN4O5) molecules surround 'Photosystems' (more proteins) in chloroplasts waiting to turn light into chemical energy. Most plants need a middleman to convert straight inert Nitrogen into a form it can be used -- a 'fixed' compound.  Fertilizers are mainly a bunch of Nitrogen compounds.  Can you be more specific?