Effects Of ZnO NPs Foliar Application On Crop Growth And Grain Qualities

Zinc oxide nanoparticles（ZnO NPs）have become one of the most widely used nanomaterials in the industry.With the increasing application and output of nanomaterials,more and more nanomaterials released into environment,which caused many unknown effects on the farmland environment and crop growth.In order to explore the effects of ZnO NPs on crop growth and grain quality,and solve the problem of low zinc content in the major food crops（wheat and maize）in the potential zinc deficiency area of the Loess Plateau,field trials of wheat and maize were conducted to compare two kinds of Zn fertilizers,including zinc sulfate and ZnO NPs.Five treatments were set on wheat in the trial,which included control,spraying zinc sulfate at jointing stage and filling stage（Zn-2）,spraying ZnO NPs at the jointing stage（ZnO-1）,spraying ZnO NPs at jointing stage and filling stage（ZnO-2）,and spraying ZnO NPs at jointing stage,heading stage,flowering stage and filling stage（ZnO-4）,respectively.Three treatments were set on maize in the trial,which included control,spraying zinc sulfate（FZn）and ZnO NPs（FZnO）at jointing stage and filling stage,respectively.The results were showed below:Spraying ZnO NPs had no significant effect on crop yield,biomass and its components,as well as macroelements,amino acids and starch content in grain,indicating that a small amount of zinc fertilizer had no adverse effects on crop growth in the calcareous soil of Loess Plateau.The zinc content and accumulation of grain of all treatments had significantly increased compared with control in wheat.The grain Zn contents with spraying ZnO NPs and zinc sulfate treatments in same two growing periods were reached 30.5 mg·kg^-1 and 28.4 mg·kg^-1,increased by 70%and 58%compared with control,respectively.The Zn content of grain treated with ZnO NPs in four periods was40.2 mg·kg^-1,which reached the recommended value for the Zn content of wheat grain.For maize,the grain Zn contents with spraying ZnO NPs and zinc sulfate treatments in same two growing periods were reached 22.1 mg·kg^-1 and 26.2 mg·kg^-1,increased by 27%and51%compared with control,respectively.The zinc content of the leaves was the highest in all organs.The Zn content of leaves with spraying ZnO NPs and zinc sulfate treatments were reached 67.9 mg·kg^-1 and 126.1 mg·kg^-1 respectively.The two zinc fertilizers showed no significant differences in other organs,but were significant higher than control.Treatment of ZnO NPs and zinc sulfate showed the same trend in microelements contents of other organs in the aboveground of maize.Treatment of ZnO NPs had no adverse effects on the growth of maize,indicating that a small amount of ZnO NPs entering the farmland environment could be used as zinc fertilizer for crop zinc addition.（2）The results ofμ-XRF analyzing of wheat grain showed that the application of ZnO NPs significantly increased the Zn content of wheat grain,which was mainly distributed in the aleurone layer and crease region.At the same time,the application of ZnO NPs extended the distribution range of Zn,the Zn content in the endosperm also increased somewhat.That appeared a great improvement for the supply of zinc in daily diets for residents who use peeled flour as the staple food in our country,and contributes greatly to alleviate the society health problems caused by zinc deficiency.There were no differences in leaf structure between different Zinc fertilizers.Surface adhesion of ZnO NPs was observed in ZnO-2 treatment,and energy spectrometer scanning determined that the zinc content in ZnO-2 treatment was significantly higher than that in Zn-2 and CK.These treatments of zinc sulfate and ZnO NPs did not have significant differences in quality of crop grain（amino acid,starch,protein and soluble sugar content）,which indicating that ZnO NPs are same to zinc sulfate,which did not have any adverse effects on crop growth.