Glycine-chelated zinc rather than glycine-mixed zinc has lower foliar phytotoxicity than zinc sulfate and enhances zinc biofortification in waxy corn

To determine whether high spraying concentrations of Zn sources increase the Zn concentration in waxy corn (Zea mays L. var. ceratina Kulesh) seeds without compromising agronomic performance, field experiments were conducted between 2018 and 2020. Excess ZnSO4 application caused foliar burn, barren ear tip, and grain yield loss. ZnEDTA and Glycine-chelated Zn (ZnGly) caused less foliar burn, but Glycine-mixed Zn caused more foliar burn than ZnSO4. The seed Zn concentration increased with spraying Zn concentration. ZnEDTA (<= 0.8%) had a higher threshold concentration than ZnGly (<= 0.4%). Nevertheless, Zn biofortification efficacy did not signifi-cantly differ between 0.4% ZnGly and 0.8% ZnEDTA, and the grain Zn recovery rate of 0.4% ZnGly was much higher than that of 0.8% ZnEDTA. Additionally, dual-isotope labelling tests confirmed that N-15-glycine and Zn-68 in ZnGly interacted. In the future, chelating technology is essential for developing new Zn fertilizers to optimize Zn biofortification efficacy.