Abstract
The purpose of this study was to examine the factors deteriorating kernel quality of rice cultivar ‘Koshihikari’ cultivated in Aichi Prefecture. The investigation was executed in 68 fields in 2006−2009. The occurrence of base immature kernels was most prominent among white immature kernels at a high temperature. On the other hand, the occurrence of milky white kernels was less than that of base immature kernels, even in 2009 which was a year with low insolation during the ripening period. Therefore, the quality deterioration of ‘Koshihikari’ in Aichi Prefecture was considered due to the occurrence of base immature kernels. Since the occurrence of base immature kernels positively correlated with average temperature and sunshine durations during the 20 days period after heading, the kernel quality of rice is considered to be greatly influenced by climate. Base immature kernels negatively correlated with the leaf nitrogen content at full heading time, the content of the brown rice protein, and the amount of the nitrogen supply, including the mineralized nitrogen in soil. The amounts of nitrogen fertilizer in the fields were 1.47 g m-2 that was insufficient compared with the optimum amount of nitrogen fertilizer. Thus, the amount of nitrogen fertilizer was insufficient for Koshihikari cultivation in Aichi prefecture. We concluded that it is necessary to increase the amount of the nitrogen supply to control the occurrence of base immature kernels.
