Variation of grain zinc, phytate concentration and phytate : Zn molar ratio in unpolished and polished rice affected by foliar zinc application among Thai rice varieties

This study evaluated the variation in grain yield and Zn concentration in rice after foliar application of Zn and the impact on its phytate : Zn molar ratio among 21 rice varieties. Rice varieties were grown under field conditions using a randomized complete block design with four replications over two cropping years in 2020 and 2021 during the rainy season. Foliar Zn application varied grain yield from −26.0 to 13.6% in 2020 and −14.7 to 30.4% in 2021 compared with non-foliar Zn. Grain Zn was varied from 0.5 to 31.1% in 2020 and from −5.9 to 47.8% in 2021 in unpolished rice and from 9.4 to 47.0% in 2020 and from 8.2 to 163.0% in 2021 in polished rice. The phytate : Zn molar ratio was decreased when foliar Zn was applied to the unpolished and polished rice, with a lower ratio in the polished rice. The phytate : Zn molar ratio decreased exponentially with increasing grain Zn concentration in the unpolished rice, while decreasing linearly with increasing grain Zn concentration in the polished rice. The results of this study suggest that foliar Zn application is a promising way to improve the grain Zn concentration and decrease the phytate : Zn molar ratio, thus being beneficial for human diets, but the effects of rice variety, cropping season, and the polishing process should be considered.