Yield of High-yielding Indica and Japonica Rice Cultivars Transplanted 3 Weeks Earlier than Conventional Transplanting in the Hokuriku Region, Is not Reduced

Abstract

In the Hokuriku region, yields and dry weights of high-yielding cultivars under early- and normal-planting were compared to verify whether the extreme early-planting around April 20 is possible. First, the15-day-old seedlings of indica cultivars “Hokuriku 193” and “Oonari” were confirmed to be more susceptible to low temperatures than the japonica cultivar “Akidawara”. In early-planting, the average temperatures during the first 3 days after transplanting were low and ranged from 7.8 to 17.3°C. In early-planting, the indica cultivars showed yellowing of leaves and death of lower leave immediately after transplanting, but the plant growth recovered with increasing temperature. Early-planting of all cultivars showed a longer lag from planting to start of growth than the normal-planting. However, due to the longer days to heading, there was no difference in the actual growing period until heading, which is calculated from the period from the start of growth to heading. Since the calendar day of heading was earlier in early-planting, the daily radiation during ripening tended to be higher in early-planting. As a result, the brown rice yield was not lower in any year or cultivar in early-planting. Therefore, this early planting technique may be a promising cultivation technique that can mitigate work conflicts in spring.