The two biggest problems for international trade are tariffs and quotas (And subsidies. Ok, three biggest problems…). These are troublesome specially when they are from countries that developed specificallybecause of international trade. It’s just shooting yourself in the foot.
Japan requires significantly high tariffs on imported rice, forcing their citizens to pay double what Americans or South Koreans would pay for their staple crop.
And although there are many other reasons to lament the Fukushima nuclear disasters, one (radioactively bright) silver lining might be the reduction in import tariffs on rice.