Zinc and iron concentrations in grain milling fractions through combined foliar applications of Zn and macronutrients

Agronomic biofortification of wheat with Zn and Fe can correct micronutrient deficiency in humans who consume wheat. In this study, two field experiments were conducted to investigate the effects of foliar Zn application combined with (1) macronutrients and Zn-amino acid chelates and (2) different soil N levels on Zn and Fe concentrations in whole grain and flour grown with straw incorporation. The results of the first experiment showed that flour Zn concentrations increased by 60.5%, 39.9%, and 56.2% due to the foliar application of ZnSO4 combined with N (urea), PK (KH2PO4), and K (K2SO4), respectively, compared to the control, and the corresponding increases in whole grain were 65.6%, 38.1%, and 50.1%, respectively. Compared with foliar Zn application alone, foliar N and K applications caused similar increases in grain Zn and Fe concentrations, whereas the foliar application of Zn combined with PK resulted in a significant decrease (approximately 12.1% across the two cropping years) in whole-grain Zn concentrations. Flour Zn concentrations, however, were unaffected by foliar Zn combined with PK fertilization and significantly increased due to the foliar application of Zn combined with N or K (in the first cropping year) compared to foliar Zn application alone. Foliar Zn combined with macronutrient fertilization tended to increase flour and grain Fe concentrations. Additionally, reducing the soil N application rate generally had a small effect on flour and grain Zn and Fe concentrations. The results of the second experiment showed that the application of Zn(Gly)2, alone or in combination with N(urea), caused similar increases in Zn and Fe concentrations in flour and whole grain. Foliar ZnSO4 combined with macronutrient fertilization under 15% reduced soil N supply and straw incorporation is an economical, effective, practical, and environmentally friendly agronomic practice for enhancing Zn and Fe concentrations in flour.