It’s not uncommon for automotive products to come up in non-related contexts, but **Blue DEF** (Diesel Exhaust Fluid) is specifically designed to reduce emissions in diesel engines and isn’t meant to be used as lawn fertilizer. While it does contain urea, which is found in some fertilizers, the concentration and other compounds in Blue DEF could actually be harmful to your soil or plants.
It's best to stick with fertilizers that are made for lawns, designed to deliver the right nutrients without the risks. Letting your neighbor know that Blue DEF isn’t safe for the lawn would be good advice, and it'll definitely earn you points as the "informed neighbor"