Zn Nutritional Quality In Wheat Grain And Its Milling Fractions As Affected By Foliar Zn Combined With NPK

Human Zn deficiency, mainly caused by insufficient dietary intake, is widely concerned by peoples in China as well as in other countries. Zn biofortification on wheat gets the most concerns of researchers not only because it provides calories and proteins for human activity,but also because it is the major source of micronutrients, such as Zn, for people in developing countries. However, the main producing area of wheat in China is Zn deficient or potentially Zn deficient soil, which producing the grain with low Zn concentration and bioavailability.Additionally, the concentrations of Zn, Fe and other minerals are further reduced during milling because most of wheat in China is consumed as flour-derived products. Foliar Zn application(with appropriate method and dose) is proposed as a rapid and effective method to improved grain Zn and bioavailability, but it has not be widely used in practice due to time and energy-consuming. Therefore, it is very important to explore the effect of foliar Zn together with NPK(widely used in practice) on Zn concentration and bioavailability, other nutritional quality and flour processing traits in grian, especially in consumed flour.Long-term field experiments were conducted in this study to investigate how foliar Zn combined with NPK affects Zn concentrations in whole grains and grain fractions and the underlying mechanism. Also, this research emphasises on the nutritional quality and processing traits in cosumed flour. The main results were obtained as below:(1) A two-year field experiment was conducted to investigate the effects of soil N(0, 120 and 240 kg N/hm2) and foliar Zn applications at different growth stages(jointing, flowering,early grain filling, and late grain filling) on Zn translocation and utilization efficiency in winter wheat grown on potentially Zn-deficient soil. The results showed that foliar Zn application at the early grain filling stage significantly increased the Zn concentration in the grain(by 82.9% compared to control) and the Zn utilization efficiency(by 49% compared to jointing). Grain Zn uptake, however, was little affected by foliar applications. The Zn concentration and uptake in the straw significantly increased with the timing of the foliar Zn application untill the late grain filling. Additionally, a high N supply significantly increased the Zn concentration in and uptake by grain and straw, but it had little effect on the efficiency of Zn utilization. Consequently, a foliar Zn application at early grain filling causes Zn tore-translocate into grain from vegetative tissues, resulting in highly nutritional wheat grain.Finally, the early grain filling stage is the desirable stage of foliar Zn application. Also, the N nutrition is a critical factor in both the concentration and translocation of Zn in wheat.(2) Field experiment was conducted to investigate the effects of foliar Zn combined with N or P on Zn concentration and bioavailability in wheat grain and its milling fractions. The results showed both high soil N supply and foliar Zn-enriched fertilizer applications greatly increased Zn concentration and bioavailability in both whole grain and grain fractions.Compared with foliar Zn alone, foliar Zn combined with N increased Zn concentration and bioavailability, whereas foliar Zn combined with P decreased Zn concentration and bioavailability. However, foliar Zn combined with P slightly increased the protein concentration compared to foliar Zn alone. Protein conc entration signi fi cantly increased,whereas phy-tate concen tration decreased, in whole grain and flour, both in soil N and foliar Zn-enriched N treat-ments. Therefore, foliar Zn plus N(with appropriate soil N management)may be a promising strategy for addressing dietary Zn micronutrient deficiencies.(3) Based on a two-year field experiment, Inductively Coupled Plasma Optical Emission Spectroscopy(ICP-OES) was used to determine total Zn concentration in whole grains and grain fractions, while Inductively Coupled Plasma Mass Spectrometry(ICP-MS) was used to analyse Zn concentration in Tris-HCl extracts, which represents soluble Zn. The results showed that foliar N and P combined with Zn resulted in much greater Zn concentration and bioavailability in whole grain and grain fractions compared to foliar N or P alone. Total Zn concentration in flour increased with foliar Zn-containing fertilizers mainly from soluble Zn,while the corresponding increase in bran was mainly insoluble Zn. Additionally, amino acid concentration tended to decrease with application of foliar Zn or P alone, but increased with foliar N.Accrodingly, Zn can be co-applied with foliar N or P and improve nutritional quality of consumed flour and whole grain to benefit human health.(4) 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 under straw incorporation conditions. 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% acrossing the two croppingyear) 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 the concentration resulted from foliar Zn application alone. Foliar Zn combined with macronutrient fertilization also tended to increase flour and grain Fe concentrations.Appropriately reductions the soil N application rates under straw incorporation conditions generally resulted in small effects on flour and grain Zn and Fe concentrations. Additionally,flour processing traits were little affected by fertilization. The results of the second experiment showed that Zn(Gly)2 caused a similar Zn concentration in both whole grain and flour compared with ZnSO4. Thus, foliar Zn combined with NPK can also improve Zn and Fe concentration in whole grain and consumed flour under straw incorporation conditions.(5) Field experiment in two locations with different soil available K levels were conducted to investigate the effect of foliar Zn combined with K application on Zn nutritional quality in both whole grains and consumed flour. The results showed that foliar Zn combined with K application significantly increased Zn concentration in whole grains under soils without K input for a long time, but not in soils with straw incorporation compared with foliar Zn alone. Meanwhile, foliar Zn combined with K application largely increased flour Zn concentration compared with foliar Zn alone under appropriate N supply, and this increase was mainly composed by soluble Zn. Foliar Zn combined with K also greatly increased Zn bioavailability in whole grains and consumed flour, additionally, flour amino acid concentration was also increased by foliar Zn combined with K. Therefore, foliar Zn combined with K is an effective method to improve nutritional quality in whole grains and consumed flour in potentially Zn-deficient calcareous soil, especially in soil without K input for a long time.In sum, foliar Zn combined with NPK application is a promising strategy to improve Zn concentration and bioavailability, maintain a higher nutritional quality(e.g. protein and amino acid concentration) in whole grains and grain fractions, as well as hold an unaffected flour processing traits in areas mainly with potentially Zn-deficient soils in China.