Not the person you are replying to, but it should be noted that synthetic fertilizer usage is lower on plant-based diets even compared to maximal usage of manure. This is due to the fact that you don’t have to grow so much animal feed (which you lose most of the energy from by other creatures body functions using that energy themselves)
shifting from animal to plant sources of protein can substantially reduce fertilizer requirements, even with maximal use of animal manure
Not the person you are replying to, but it should be noted that synthetic fertilizer usage is lower on plant-based diets even compared to maximal usage of manure. This is due to the fact that you don’t have to grow so much animal feed (which you lose most of the energy from by other creatures body functions using that energy themselves)
https://www.sciencedirect.com/science/article/abs/pii/S0921344922006528
While any food production is not going to be free of environmental effects, plant-based diets are substantially better on nearly all metrics