The Estimation of an Effective Cumulative Temperature for Emergence of Rice Cultivar ‘Koshihikari’ without Heating in Ishikawa Prefecture

[摘要] A technique has been developed for transplanting densely-seeded seedlings. The range of leaf age suitable for transplanting is narrow in these seedlings. This limits the acceptable range of the nursery period. In addition to heating nursery boxes till emergence, a conventional method, keeping those unheated under outdoor or greenhouse conditions may produce various periods to emergence which could be utilized to adjust the nursery period. Clarification of the thermal time required for emergence could help us estimate the period from seeding to emergence. The objective of this study was to clarify the effective cumulative temperature required for emergence and to clarify the climate factor affecting nursery box temperature under a covering material. We investigated the period from seeding to emergence in nursery boxes kept unheated under outdoor and greenhouse conditions from the beginning of April to the beginning of May. We also measured the hourly temperature of each nursery box under a covering material. The period from seeding to emergence was 7-18 days and 5-8 days under outdoor and greenhouse conditions, respectively. The smallest coefficient of variance, 63°C, was obtained, when calculated with the base temperature at 8.7°C. Heat shielding material kept the temperature under the covering material <40°C.The daily mean temperature under the covering material significantly and positively correlated with that of the surrounding atmosphere suggesting that day of emergence can be estimated from the surrounding air temperature.

[学科分类] 农业科学（综合）

[关键词] Effective cumulative temperature;Emergence;Emergence without heating;High-density seeding;Rice