Aze-mame, 畔豆, Japanese word literally means "Dike-bean". In Japan, it is common to grow Soybean on the dike of paddy field together with rice. I saw it in Sichuan, China too, and recently from one of Frickr friend's photo stream, I saw it in Philippines, although the bean appears to be kidney bean.
So now I am wondering this Aze-mame would be common East Asian traditional method. Off course, leaves and stalks, nitrogen rich by nitrogen fixing ability of bean plants, will be fed to the paddy field as fertilizer. And beans is protein rich foods, assisting rice eating people. Perfect man-nature sustainable system!!
Soybean contains rich protein so, rice and soya bean provide people with balanced nutrient. Like cattle, soya bean utilized various foods, especially through fermentation, miso (soybean paste), natto, soya sauce and even cheese. As raw, various form of tofu and soya milk is also very common among Chinese and Japanese.
Tsukuba, Ibaraki, Japan, July 2007