Biofortification and estimated human bioavailability of zinc in wheat grains as influenced by methods of zinc application

Background and aims Agronomic biofortification of Zn requires an effective Zn application method and efficient Zn utilization by the crops. Various Zn application methods were compared for Zn biofortification in grains of wheat grown in a calcareous soil under glasshouse conditions. Methods Wheat (cv. Shafaq-2006) was treated with different Zn applications to soil (0, 4.5 or 9 mg Zn kg(-1)), seed (100 mL of either 0 or 6.75 % Zn w/v sprayed on 1 kg seed) and foliage (distilled-water-sprayed control, 1 mL of 0.05 % Zn w/v at jointing, 2 x 1 mL of 0.50 % Zn w/v at heading or combined jointing and heading sprays) in all possible combinations. Mineral (Zn, Ca and Fe) bioavailability to humans was estimated based on phytate-to-mineral molar ratios. Zinc bioavailability was also quantitatively estimated using trivariate model of Zn absorption. Results Soil Zn application increased grain yield (29 %), whole-grain Zn concentration (95 %) and whole-grain estimated Zn bioavailability (74 %). Foliar Zn application at heading also increased Zn bioavailability, but progressively less so with incremental soil Zn rates. Soil Zn application increased grain concentration and bioavailability of Ca, but decreased them for Fe. Conclusion High soil Zn application increased estimated Zn bioavailability to humans. Also, medium soil Zn rate may be combined with foliar Zn sprays at heading where high soil Zn application is not feasible because of economic or environmental reasons.