The effect of air temperature and solar radiation on the occurrence of chalky rice grains in rice cultivars “Koshihikari” and “Akitakomachi”

Global warming has already affected agricultural production worldwide. In Japan, the occurrence of chalky rice grains (CRGs), which are low quality grains whose occurrence is exacerbated by high air temperature, has become a major issue. There is concern that this occurrence will become more frequent with increasing global warming; therefore, it is necessary to develop a model that can accurately estimate the impact of global warming on the occurrence of CRGs. In this study, such a model was developed for Japan's main cultivars, "Koshihikari" and "Akitakomachi". This model is a non-linear model and was also used to investigate the differences in the responses of these cultivars to temperature and radiation; the occurrence of CRGs was explained as a function of air temperature and solar radiation in this model. The results showed that the occurrence of CRGs could be reproduced more accurately when both air temperature and solar radiation were considered compared to when only air temperature was considered; the latter is the case with existing models. The air temperature at which CRGs begin to appear is lower for "Koshihikari" than "Akitakomachi", when the average solar radiation is small (less than 16.4 MJ m(-2) d(-1)). The proposed model will hopefully be applied to impact assessments of global warming and the quantification of varietal characteristics with respect to the occurrence of CRGs.