Impact of foliar and root application of phosphorus on zinc concentration of winter wheat grown in China

Foliar zinc (ZnSO4) application is an effective agronomic tool for Zn biofortification of wheat (Triticum aestivum L.) and hence for overcoming human Zn deficiency. It is unclear how the methods used to apply phosphorus (P) fertilisers affect the uptake and availability of Zn in wheat plants. Here, a solution-culture experiment and a 2-year field experiment were conducted to determine the influence of P applied to leaves or roots on total, soluble and insoluble Zn in winter wheat plants (cv. Xiaoyan-22) also receiving foliar Zn. Foliar Zn application, regardless of P application, significantly improved grain total Zn (primarily water-soluble) by 79.4% under both growth conditions, and reduced grain phytic acid : Zn (PA : Zn) molar ratio by 54.4% in the field. In solution culture, root-applied P did not affect plant uptake of foliar-applied Zn; however, foliar application of Zn plus P reduced the soluble fraction of Zn in wheat tissues, and thus decreased grain Zn concentration by 13.2% compared with Zn-only foliar application. Similarly, in the field, foliar-applied Zn plus P resulted in lower grain total and soluble Zn concentration and higher grain PA and PA : Zn molar ratio than foliar Zn alone. Overall, foliar Zn application is efficient in increasing grain Zn concentration and bioavailability under varied methods of P application. Although foliar-applied P slightly reduces the ability of plants to use foliar-applied Zn to increase grain Zn, foliar Zn combined with commonly applied foliar P application represents an easily adoptable practice for farmers that will help to alleviate Zn deficiency in human populations.