The reality is that 100 years ago we didn't use fertilizer and we were running out of food. We also mined the soils in western Canada in the 1930s. We had terrible soil loss, partly due to drought but also to the fact that the soils were completely depleted. We grew crops year after year, and there was nothing going back in. We took the crops out, but we didn't put anything back in.
The way the world works, you can't do something with nothing. Yes, our products have a carbon footprint, which we're trying to reduce. Yes, there is a cost to growing food. However, we also have an imperative to grow that food for people, for economic development in Canada, and to feed people around the world.
There isn't enough manure and there aren't enough other sources of non-fertilizer nutrients to feed the population that we have now, and there is certainly not enough of those materials to feed the 9.6 billion that we expect to have. We're probably going to have to make some choices about where we spend carbon. I would say that feeding people is probably a better choice than some other choices in society about where we use carbon. I don't think there's any future that we can foresee where simply reducing fertilizer use is going to have a good outcome for humanity.