The main component of eggshells is calcium carbonate, which has been used for Ca research in rice cultivation in Japan. The effectiveness of Ca ions on rice was discovered in the 1 960 s by means of hydroponics, but the effect of Ca application on soil-grown rice has not yet been studied. The high-temperature ripening disorder of paddy rice in Japan in recent years is a sterility phenomenon caused by the failure of assimilation products produced in the leaves to be transferred to the ears. Therefore, to maintain the translocation of assimilated products produced in rice leaves, supplying Ca continuously even in small amounts is more important than increasing the Ca concentration in the plant. If research can be conducted on not only calcium carbonate, the main component of eggshells, but also the translocation rate of assimilates in paddy rice, and if high-temperature ripening disorders caused by weather conditions can be avoided, eggshells can be used as an agricultural material that contributes to food security in Japan.
