Effective Heat Unit Summation and Base Temperature on the Development of Rice Plant II. On heading, flowering, kernel development and maturing of rice

Abstract

Rice Plants were grown under different controlled temperatures in order to analize the effective heat unit summation (EHUS) and base temperature (BT) for the specific stages of reproductive phase in accordance with the method described in the previous report. BT for the emergence of panicle and flowering of cultivar Sasanishiki was 12.1°C and 11.5°C, respectively. In the ripening period, BT showed its highest value of 9.4 to 10. 1°C at the ealiest stage, declining to’ 4 to 5°C toward the latest stage of ripening. BT of an indica rice (Ko-Sen) was 0.6-2.7°C higher than a japonica rice (Sasanishiki) throughout the ripening period, although EHUS was on the contrary obviously less than that of japonica one. It was thought therefore that indica rice requries a higher range of temperature and a lesser amount of effective heat for its kernel development as compared with japonica one. BT and EHUS for the entire period of kernel development of a japonica rice was 7.5°C and 690°C • days, respectively. Reasonability of these values was supported by a result calculated from the experimental report on rice crop situation in Japan 1973-1977. BT relating to the development of rice plant changed with the developmental stage showing its peak of 12 to 13°C at the stage from flag leaf emergence to heading. © 1990, CROP SCIENCE SOCIETY OF JAPAN. All rights reserved.