Back to crop rotation, traditional farming methods and less reliance on fertilizer equals lower yields but not no yield.
Of course it's not no yield, but the point is the worlds population is sustained by the yields we do get from the way we do things now. The CEO of one of the worlds largest fert manufacturers was saying approx half the worlds population is sustained by the yield from fertilizer.
I know this'll make the "the world needs a cull anyway" people happy, but the reality of that sentiment isn't going to look pretty.