1. The production cost is much cheaper here than in China. The most part of the price of the rice in suppermarkets is the distribution cost . And the international transportation fee is not a big deal compare with the price of the goods if you use big vessels(imazing the coal and ore that are in the same situation)
2.There are 75 to 80% Chinese live in countryside, if they lost their "jobs", what will happen there?
3. The fields will become barren if none plent on for several years. For some reasons in future, if North American can not or will not sell grains to China, where can Chinese find enough food for its 1.3 billion pople?