Relations between Constituents of Rice Yield and Meteorological Factors (IV)

Examples at Mogami-gun Area, Yamagata

Abstract

In this paper the author studied the dependence of the yield in rice on weather conditions to find more reasonable reasons for the recent increment in the rice yield. The data on the rice yield at Mogamigun (Yamagata Prefec.) and on the weather conditions at Shinjo were analyzed statistically. The following may be summarized:
1. The recent increase in the rice yield was mainly attributed to the increase of the number in rice panicles per unit area. The increase in the panicle's number was not due to the increase in tillers per hill but due to the increase of the plant density.
2. Both the numbers of panicles per hill and spiklets per panicles were almost constant during recent ten years. The percentage in the ripened grain increased due to both the recent development in agricultural techniques and the recently favourable weather conditions.
3. The correlation coefficient between the yield and a monthly mean air temperature was highest in July. Contray to the expectation that the influence of the mean air temperature during this stage on the generative growth of rice plant should decrease due to the application of the improved techniques, the correlation analysis indicated that the weather dependence of the generative growth was increased that is, the correlation coefficient increased from 0.582 to 0.767 or 0.793. (see Table 1)