…the rice yield per hectare in Japan, after climbing for more than a century, has not increased at all over the last 17 years. It is not that Japanese farmers do not want to continue raising their rice yields. They do. With a domestic support price far above the world market price, raising yields in Japan is highly profitable . The problem is that Japan’s farmers are already using all the technologies available to raise land productivity.
Like Japan, South Korea’s rice yield also has plateaued.
…Rice yields in Chin are now very close to those in Japan. Unless Chinese farmers can somehow surpass their Japanese counterparts, which seems unlikely, China’s rice yields appear about to plateau. If China hits the glass ceiling for its rice yields, then one third of the world’s rice would be produced in three countries (Japan, South Korea, and China) that can no longer raise land productivity or expand the area in rice.
That is from the new, excellent and to the point Full Planet, Empty Plates: The New Geopolitics of Food Scarcity, by Lester R. Brown.