Effects of foliar iron application on iron concentration in polished rice grain and its bioavailability

Iron (Fe) deficiency in humans caused by inadequate dietary intake is a global nutritional problem. A glass house pot experiment was conducted to evaluate the effect of foliar FeSO₄ containing applications on concentrations of Fe, Zn, and Fe bioavailability in polished rice among five rice cultivars. The results showed that foliar application of FeSO₄, FeSO₄, plus nicotianamine (NA), and FeSO₄ plus NA with ZnSO₄ increased the grain Fe concentration by 16.97%, 29.9%, and 27.08%, respectively. The grain Fe bioavailability also increased by foliar application of FeSO₄, FeSO₄ plus NA, and FeSO₄ plus NA with ZnSO₄; these represent increases of 12.63%, 20.86%, and 18.75%, respectively. Foliar FeSO₄ containing applications improved the Fe bioavailability and might be attributed to the reduction of phytic acid and the increase of Fe concentration in polished rice. Addition of ZnSO₄ to foliar Fe application increased both Fe and Zn content without altering Fe content and bioavailability. In addition, the cultivar difference in Fe and Zn concentration was observed and may be due to the genetic control of leaf absorption and seed deposition of foliar application. Furthermore, the cultivar difference in Fe bioavailability observed might be attributed to the variation of grain Fe, phytic acid, and total phenolics contents among the five rice cultivars. The results suggested that foliar FeSO₄ containing applications represent a promising agricultural approach to reduce Fe deficiency in countries where polished rice is extensively consumed.