Food or fertilizer? If you want FOOD that you eat then your ONLY hope is certified organic food. And that may not work either because animal poop is considered NATURAL.
Urea fertilizer is as old as human kind and was the only kind of fertilizer until this past century when food production became wide scale.
Your grand parents who worked the farm used urea fertilizer because the cows and sheep make the stuff every day. And using it for fertilizer was a handy use and way to get rid of it or the poop would be piling up everywhere. Sheep dung is a very powerful fertilizer.
Not sure why you worry about it. Chemical fertilizers using potash are what you should be concerned about.
Animal poop is about as natural as it gets.