Zinc (Zn) application methods influences Zn and iron (Fe) bioavailability in brown rice

Abstract

In this study, we evaluated the possibility of increasing Zn and Fe bioavailability in twenty-six popularly grown rice cultivars by external application of Zn through soil and/or foliar means. A field experiment was conducted in an Inceptisol applying Zn through soil and/or foliar means and the harvested whole grains were processed to brown rice and subsequently analysed for Zn, Fe, phytic acid and crude protein contents. Native Zn concentration in the brown rice of those tested cultivars varied from 22.9 to 79.7 with a mean of 40.3 mg kg−1. Zn concentration in brown rice increased to the tune of 17 and 95% upon Zn application through soil and soil + foliar, respectively, over the control across the tested cultivars. Zn application further caused a decrease in the phytic acid/Zn molar ratio to the magnitude of 64.0 and 23.0% upon soil + foliar and sole soil application, respectively. The decrease in phytate/Zn molar ratio was higher in high yielding varieties followed by local varieties, aromatics and hybrids and thus increased the bioavailability of Zn in brown rice. An antagonistic effect was also observed on the iron content in brown rice upon application of Zn. The decrease in iron concentration in brown rice was higher with soil + foliar application than with only soil application of Zn. Zn application through soil + foliar over basal application could be a useful strategy to produce Zn dense grains and to reduce the phytate/Zn and phytate/Fe molar ratios and thus enhancing their bioavailability. Application of Zn fertilizers can also enhance crude protein content in brown rice.