It isn't nitrogen, it's lead. Lead is needed in regulatory proteins, like calmodulin. Plants grow very quickly without it, then fall over.

At micromolar concentrations this may be true. There is plenty of Pb to go around in the soil and in the air from private aviation for such a minor micronutrient. I also doubt elevating Pb levels in crops is at the top of many public health agendas.

It should be. It has the same effect on people - they grow too much too fast, but remain immature and fragile both mentally and physically. They do hit puberty very early though.

Calmodulin needs calcium, not lead.