Lets not forgot to mention that power hungry politicians have grabbed the power away from businessmen and entrepreneurs and put them into a regulation straight jacket.
A farmer, who consumes most of his harvest (of course he has an urgent need for the crop) and does not reinvest enough of the seeds into the next crop will gradually produce less and less. Of course for a while, he can borrow seeds from another well managed farm, but that does not reverse the downtrend.