Effects of Climate Factors on Regional Differences in Yield from the Viewpoint of Change over the Years in Rice Cultivation in Japan

Abstract

The relationship between temperature and solar radiation during the growth period, with the yield and yield components was analyzed. The 5-year average climate and yield data for 1963–1967, 1988–1992 and 2014–2018 in 41 prefectures were taken from data provided by the Japan Meteorological Agency and Ministry of Agriculture, Forestry and Fisheries. Average temperature(T) and average solar radiation(S) from 29 days before heading to heading and that from 1 to 30 days after heading were calculated as T2 and S2, respectively, and T3 and S3, respectively. Among these climate factors, T2 was the most closely related to yield. T2 was negatively correlated with the total spikelet number per area and yield in the comparison of 41 prefectures in every 5-year average. The tendency of increase in yield as temperature decreased in the comparison among prefectures became stronger over the years. This suggests that the negative effect of high temperature on the regional differences of yield increases over the years by the nationwide improvement of cultivation technique and the increase of temperature during the growth period. On the other hand, in each prefecture, the year with high temperature showed higher solar radiation and higher yield. This suggests that the high temperature caused by global warming may not always decrease yield if the solar radiation increases accordingly.