Biofortification of wheat with zinc as affected by foliar applications of zinc, pesticides, phosphorus and biostimulants

Integrating foliar zinc (Zn) application into common practices, e.g. application of pesticides, phosphorus (P) or biostimulants, is a feasible agronomic strategy of wheat biofortification. However, it remains unclear how this integrated approach affects the efficacy of foliar Zn sprays, especially under unfavourable environmental conditions. Here, two field experiments considering Zn forms (ZnSO4 and zinc-glycine) and applications (alone or combined with pesticides, KH2PO4, and biostimulants amino acids or fulvic acids) were conducted in two seasons (2017 and 2018), and their effects on the magnitude of grain Zn increment and bioavailability were evaluated. The results showed that less precipitation in 2018 caused 11.7-52.2% yield losses than in 2017, which increased grain Zn concentration by 13.4-58.4%. Foliar application of Zn-glycine did not surpass ZnSO4 spray in regarding to grain Zn concentration and bioavailability. Grain Zn concentration substantially decreased in plants sprayed with KH2PO4 irrespective of Zn forms applied, indicating strong antagonistic effects of P supply on grain Zn enrichment. There were no differences in grain Zn density between the applications of amino acids and fulvic acids. However, grain Zn bioavailability significantly increased by 22.3 and 23.4% in the Zn plus pesticides treatment when sprayed with fulvic acids in 2017 and with amino acids in 2018, respectively. Overall, environmental conditions and foliar Zn management considering Zn forms and applications accounted for 35-45% and 20-37% of explained variation in the magnitude of grain Zn increment, respectively. The results demonstrated that management and environment are crucial factors to consider in agronomic biofortification of wheat.