Accepted 1^st September, 2019
 
Satoko Yasumoto*, Makoto Kojima, Natsumi Okamura, Hiroko Sawada and Morio Matsuzak

National Agriculture and Food Research Organization (NARO), Central Region Agricultural Research Center, 2-1-18 Kannondai, Tsukuba, Ibaraki 305-8666, Japan.

To improve Japan’s international agricultural competitiveness, we directed our attention to lowering the cost of rice cropping by direct-seeding in drained fields. To support the introduction of direct-seeded rice cultivation, we compared the variability in developmental stages from seeding date in direct- seeding cultivation with that from transplanting date in transplanting cultivation to ripening. We used eight cultivars with wide differences in maturity, from very early to mid–late. The variability in the number of days from direct-seeding or transplanting to ripening with cropping seasons tended to decrease greatly from mid- to late-maturing cultivars but small for very-early-maturing cultivars. As direct-seeded rice is easily affected by environmental factors, especially from direct-seeding to heading, then the variability in the duration between years was larger in direct-seeding cultivation than in transplanting cultivation. But the tendency to decrease with cropping season was similar between cultivation methods. The variability of the duration for ripening phase with cropping seasons was similar between the methods in plants that headed together. It was thought from these results that the knowledge about the developmental stage variability with cropping seasons of transplanting cultivation can be applied to direct-seeding cultivation and can provide the groundwork needed to support the introduction of direct-seeding cultivation.

Key words: Oryza sativa, direct-seeding cultivation, transplanting cultivation, cropping season, developmental stages, rice.