The whole idea behind that was that (within reason) the more N you can pump into the crop, the more it will yield, but also the taller it will grow. Wheat is essentially an inverted pendulum when ripe, with about 60% of the above-ground biomass perched at the top.
The main thrust of modern crop breeding has been to create crops that you can successfully get to harvest under high-nutrition environments, without it literally falling over or succumbing to disease due to the turgid, fleshy growth. Even then, if you're applying more than maybe 150kgN/ha, you will be relying on plant growth regulators that inhibit auxin/gibberellin response to keep the plant under control.
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.