Koden (run-down field) is the term indicating fields that had been cultivated but have been abandoned for some reason during the ancient times and middle ages.
Opposed to this, non-cultivated, undeveloped lands were called Kochi, and property made temporarily unavailable due to disasters was called Sonden to distinguish the difference.
The reasons for Koden were various and can be largely divided into cases due to physical aspects of the property itself, such as poor soil, and cases due to natural disasters such as flooding (Kawanari).
Under the Ritsuryo system (a system of centralized government based on the ritsuryo code), they were also called Kohaiden or Fukandenden. 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. There was a push for redevelopment and maintaining fields, so Jyokoden were chinso (leased to farmers, 6 years for Koden and 3 years for Shiden under the Ritsuryo system) and benefits were given to those who requested. However, with the enlargement of Shoen (private estates) in the Heian period, it became harder for the Kokushi (officers of local government) to collect taxes and there were cases where kokushi would report such property as koden. Later, prominent farmers or local bureaucrats used this rule to redevelop Koden and make it private property (resident landholder system).
Furthermore, in the middle ages, the establishment of Myoden (rice field lots with a nominal holder) and the introduction of "ronin" accompanying environmental improvement by kokuga (provincial government offices) and shoen landholders led to active development of Koden. On the other hand, property with low agricultural productivity could not sustain continuous cropping and property that was deliberately cultivated on alternate years was called Kataarashi. The property in fallow years for Kataarashi were used as grazing land but it was hard to plow and restart (called Aratauchi) such property for agricultural use. Therefore, properties that were Aratauchi were in some cases allowed rights usually given to new fields.