According to the Denryo (law on rice fields), Koden that have been left for less than 3 years were called Nenko, those left for a longer period were called Jyoko.
田令によれば、荒廃して3年未満の荒田は年荒（ねんこう）・それ以上のものは常荒（じょうこう）と呼んだ。、