Interesting...
Actually, any urine that comes directly from a urinal tract of a healthy human (perhaps many other mammals) is STERILE!
Only later, when bacteria infiltrate (literally) and start to decompose ammonia, some protein residues and whatever, (dunno the exact composition of human urine) this kind of liquid gets "infected"... and hence starts to decompose and smell real bad, as we know.
In first aid, it's well known that urinating directly over a wound or burning is the best thing you can do (in case of emergency and without classical means) to clean and sterilize a wound! In some cultures, drinking fresh morning urine, is a kinda wired (for some extremely disgusting) but quite well known and commonly accepted custom (actually cure or therapy)!
To really know if it is wether useful, beneficial or rather inadequate or even inappropriate as an ADDITIVE in a
nutrient solution, one should A. investigate it's exact composition in terms of NPK, other macro- and micro-
nutrients. And B. inquire about it's behavior in a solution in different quantities - a shot of it (which will perhaps not lead to any smell or other negative influence) might have a very different effect as a large quantity. Surely the ammonia part will not decompose properly, but in many recipes, there is a certain part of ammoniacal nitrogen anyway. The quantity will also determinate if it may interfere with the balance of the nutrient composition. Btw: A nutrient is never 100% balanced - as it's composition anyway changes permanently due to irregular absorption of different elements ( as in during the 10 days it remains in the reservoir).