Rice agriculture was paramount in Japan throughout most of it's history. The Colombian Exchange and the introduction of new crops opened up new tracts of land unsuitable for rice production, but well suited to crops such as the Andean sweet potato. The resulting increase in harvest, which roughly coincided with the Tokugawa Shogunate, an unprecedented era of peaceful isolation, conspired to create a population boom that greatly increased the population of Japan.

'1493: Uncovering the New World Columbus Created' by Charles C Mann has some great information on this topic.