The FT talks about a worrying trend to restrict global trade in food.
Countries are reducing import tariffs (a good thing) but to maintain some semblance of control over their food supplies, they are propping up export tariffs, which is bad. By reducing foreign competition (because countries aren't exporting as much), such export taxes on a global scale could have the impact of driving up local prices and limiting local supply.
If no supply is coming in from abroad, local producers of a restricted item (say corn or rice) will have an incentive to limit local production in order to drive prices up and make more profit.
I can hardly bemoan a poor farmer trying to make a healthy profit, but the end result is more hardship across a society. With a profit-maximizing farmer reducing supply, there is obviously less food to go around which increases prices and, ultimately, misery.