A Consideration on the Climatic Productivity of Paddy Rice in the Northern Districts of Japan

Abstract

An index of the climatic productivity of paddy rice was firstly proposed by Murata (1964) using the average of daily mean air temperatures and that of daily insolation amounts during the productive period of rice of 40 days from 10 days before to 30 days after heading time. However, the yield is affected by climatic conditions during the whole growing period of the plants. Therefore, we attempt to look for the index which contains climatic elements covering the whole growing period. We already analysed the relationships between climatic conditions (air temperature and duration of sunshine) and ripening with in 40 days after heading time, and obtained a climatic index ripening, YG.In this report, we have analysed the relationships among the rice yield, the daily mean air temperatures, θ6·7 and the total durations of sunshine, S6·7 by Jordan's recorder in the main growing areas in the northern districts of Japan for June and July, namely, transplanting period and heading time. Yield is affected considerably by θ6·7, but not by S6·7, as shown in Fig. 1. Thus, the lowest critical conditions of rice yields, 400, 500, 550kg/10a, could be obtained from the relations among θ6·7, S6·7 and yeields in Fig. 1, a yield of 500kg/10a may not be attained below the critical curve of 500kg/10a at all.Further, the relationship between θ6·7 and YG is analysed, and a θ6·7-YG co-ordinate which indicates the climatic conditions during the whole growing period is constructed. The climatic data of each area in the northern districts of Japan in recent years are plotted on this coordinate with yield data. Three critical curves mentioned above are obtained using the same method as in Fig. 1 (Fig. 2). Fig. 3 shows the relative situation between the values of the co-ordinate for normal years in these areas and the critical curves. It is considered that the greater is the diffeerence of the relative situations between the normal yield and the critical curve, the greater is degree of inhibition of yield by other factors than climatic ones.