This made me go down a rabbit hole of techniques for separating sodium and chloride from urea/ammonium/ammonia solutions. I wonder if it could ever be made viable when compared to the Haber process for ammonia production.

Also, phosphorus is the more scarce fertilizer, I think. I remember reading a paper from a Chinese lab that was trying to figure out how to cheaply isolate phosphorus fertilizer from commercial pig farm feces. They decided it wouldn't be cost effective.