Agronomic biofortification of zinc in rice: Influence of cultivars and zinc application methods on grain yield and zinc bioavailability

Abstract

Zinc biofortification in rice can be improved by altering Zn application timing and placement and cultivar choice. We made a comprehensive assessment on this, analysing Zn, Fe and phytic acid in whole grains and processed brown, white and cooked rice obtained from six cultivars raised with Zn applied through soil and/or foliar supply at different phenological stages of the crop and measuring Zn bioavailability in cooked rice. Pathways for Zn enrichment (27.4–92.6% over control) by Zn fertilization with different application protocols and cultivars were elucidated. Such enrichment of Zn was associated with depletion in Fe (6.5–29.4%) and phytic acid (14.8–30.4%). However, the loss of Zn on processing of rice grains increased on Zn fertilization (12.6–28.7 mg kg−1) because of a preferential allocation of applied Zn into bran and aleurone of the grains. Despite such loss, application of Zn caused a net increase in Zn bioavailability (52.2% over control) in the cooked product. Using the ranksum scoring technique, we found cultivar GB 1 and Zn supply through soil (basal) + 2 foliar applications achieved the most effective biofortfication of Zn in rice by optimizing grain yield, and enriching Zn and its bioavailability in cooked grain with least antagonism of Fe availability.