2026 Volume 95 Issue 1 Pages 91-98
An average temperature during the ripening period below 23.6ºC is appropriate for improving brown rice quality of brewer’s rice cultivar ‘Ginnoyume’ in Kochi prefecture. In this study, we estimated the transplanting time to meet this criterion in each production area. Using a model for estimating heading stages and the agro-meteorological grid square data, we calculated the first transplanting date that meets this criterion in a normal year (early limit) and found that the current transplanting date in 8 areas was earlier than the early limit. Also, we calculated the last transplanting date before the first day when the daily mean temperature was 15ºC or lower (late limit) and found no areas where the early limit was later than the late limit. Furthermore, the estimated ratios of yield and protein content at the early limit to the current transplanting date in each area were 93-108% and 102-111%, respectively. However, the ratio of production value was 98-128%, and only one area exceeded the 7.3% protein content target.
These results enabled us to estimate in which areas and for how long the transplanting time should be delayed to improve the brown rice quality of ‘Ginnoyume’. In areas where the transplanting time was delayed appropriately, poor ripening due to low temperatures could be avoided, and such a delay had little impact on production value or protein content.
