Can the Cropping Schedule of Rice Be Adapted to Changing Climate? A Case Study in Cool Areas of Northern Japan.

Adaptation of cropping schedules in response to climate change is essential for increasing rice productivity.  In the present study, we analyzed yield, cropping schedule and cultivar characteristics records from 1958 to 2007 in a case study of four prefectures in northern Japan, where low temperatures can severely limit rice growth.  Grain yield in all prefectures increased over time, with a higher increase from 1958 to 1982 (2.4 g m^-2 y^-1) than from 1983 to 2007 (1.0 g m^-2 y^-1).  The transplanting date became 0.07 to 0.91 days y^-1 earlier before 1983, but did not appear to change thereafter.  The growing period duration from transplanting to harvesting increased over time, especially during the first 25 years.  We observed a significant correlation between grain yield and transplanting date before 1983.  The length of the potential growing period, defined as the period from the earliest potential date for transplanting and the latest potential date for harvesting, increased over time in all four prefectures.  The gap between the actual growing period and the potential growing period increased after 1983.  The safe reproductive period, which is defined as the duration within which rice can escape cold damage during its reproductive stage, did not appear to change over time.  Based on these results, we discuss future cropping schedules capable of increasing rice productivity under a changing climate in the future.