To elucidate fertilizer responsiveness of rice cultivars as Akenohoshi and Nishihomare which were bred to obtain many grains in number per uni tarea, the comparisons of the form for light-interception and sink-source ratio between these and 9 cultivars including IR24 and Suweon 258, which had high fertilizer responsiveness, were carried out on three nitrogen levels (8, 14, 22kg/10a). The results were as follows; 1) Suweon 258 and IR24 had thin and short leaves which had large angle between leaf blade and the level, and then had small light extinction coefficient which could contribute to large light use efficiency. On the other hand, Akenohoshi had thick and long leaves which had small angle, and then had large extinction coefficient. The characteristics of Nishihomare were mediums. 2) The sink-source ratio of Akenohoshi was the largest. That of Nishihomare was the second from lowest sink-source ratio of Hoyoku. Those of Suweon 258 and IR24 were mediums 3) It was clarified that Nishihomare had not enough sink size at all and Akenohoshi had a problem for the form for light-interception. Consequently, it is necessary for ideal cultivars in warmer area in future to have large sink size, higher sink-source ratio, and good form for light-interception.
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