This is where I wish we were as big as Reddit. There when it was good you could ask a question like that and there would be scientists in that field, technicians doing the work — farmers in this case — answering you and getting a thousand up votes

Here you get people like me who came here because Reddit lost its soul, along with people who don't fit in well enough, discriminated groups, and open source and/or political true believers

I think you're right though. Plants need fertilisation to grow. The list of chemicals they need is the list of chemicals in animal waste. The ecosystem loops

Energy comes in through sunlight feeding plants, animals eat plants, extracting the energy and whatever else, animals dump what they don't need (and give back the balance when they die), other animals eat animals for the energy they contain and dump the waste on the ground

If you take the animal feedback out, you break the cycle, the nutrients are eaten a distance away and the waste is never returned. The plants can waste energy there's always more sunshine but they need those chemicals that were taken out of the loop. I imagine synthetic fertilizers will miss something that animals would have given back. They will be inferior.