Effects Of Foliar Zinc Application On Zinc Enrichment Of Wheat Grain Under Different Soil Nitrogen And Zinc Application Conditions

Zinc is an essential micronutrient for human body,and zinc deficiency will seriously affect human health,affecting about 1/3 of the world’s population.Wheat and its products are the staple food of half of the Chinese people.The main reason for the deficiency of Zn in the human body which takes wheat as the staple food is the low content of Zn in the grain.Studies on Zn application and interaction between Zn and Zn indicated that the combination of soil application of Zn fertilizer,especially foliar application of Zn fertilizer and other nutrient management measures,could not only achieve stable wheat yield and high yield,but also achieve the goal of rich Zn in grain.However,under different soil fertility levels of potential calcareous Zn-deficient soils,the effect of Zn and Zn combination on grain Zn enrichment and the effect on Zn storage protein remains unclear.It is of important scientific significance to reveal that soil application of Zn fertilizer,the combination of N fertilizer and foliar spraying of Zn combined with wheat grain Zn enrichment effect,and the improvement mechanism of grain nutritional quality.Therefore,we conducted two spraying experiments on wheat in two seasons based on two field location experiments.The first was to reveal the effects of combined application of organic fertilizer-Zn fertilizer and spraying on the available Zn content in calcareous potential Zn-deficient soil and grain Zn-rich.The second aim was to find out the effects of spraying Zn at different N levels on the grain Zn nutritional quality and the content of Zn storaging-related proteins,in order to provide a scientific basis for improving the grain Zn nutritional quality of wheat in calcareous soils with potential Zn deficiency.The main results are as follows:（1）A localization experiment was carried out between soil Zn fertilizer fields for 4consecutive years（4 treatments:no Zn,CK;Zn,Zn alone;Single application of organic fertilizer,M;On the basis of Zn and organic fertilizer combined application,Zn+M）,wheat spraying experiments showed that application of Zn alone or Zn and organic fertilizer combined application compared with CK significantly increased the effective Zn content from 0.76 mg kg^-1 to 3.75 mg kg^-1 and 4.73 mg kg^-1,respectively.The soil available Zn content was not significantly affected by organic fertilizer application alone,but the soil available Zn content was significantly higher when Zn combined with organic fertilizer application alone.The available Zn content in soil increased year by year.Although the soil Zn supply capacity was significantly improved,the Zn content of grains under Zn and Zn+M treatments was only increased by 18.94%～36.12%,which still failed to reach the target of grain Zn enrichment.However,compared with soil application of Zn fertilizer,the Zn content of wheat grains after foliar spraying of Zn was significantly increased and reached a significant level.The average Zn content of wheat grains under the four treatments after spraying of Zn was 54.42 mg kg^-1,which indicated that the grain was rich in Zn.In conclusion,in the calcareous soil,the Zn content of wheat grains cannot reach the standard of Zn enrichment even if the Zn supply capacity of soil is improved to a higher level by continuous Zn source application,and the foliar spraying of Zn is still the main way to achieve the Zn enrichment of wheat in the calcareous soil.（2）A 2-year wheat spraying experiment was carried out on the basis of three different N treatments(N₀,N₁₂₀,N₂₄₀,respectively),which were applied in the field starting from 2002.Regardless of the N inputs,foliar Zn application could significantly increase the Zn concentration in grains and flour by 0.95 and 1.12 times respectively,but there was no significant difference between N₁₂₀ and N₂₄₀.Compared with N₀,the N inputs increased the translocation of N and Zn,but reduced the transfer ratio of the two:N decreased from 60.2%to 48.6%and Zn decreased from 42.3%to 26.5%.Regardless of Zn₁ or Zn₀,the translocation of N and Zn in vegetative organs after anthesis and the content of N and Zn in grains showed a significant linear positive correlation.Compared with the early filling stage,the content of storage protein（gliadin and glutenin）in grains and flour at the mature stage increased significantly,accounting for about 80%～84%of the protein content.The content of gliadin and glutenin in grain and flour was increased by N application more than that of albumin and globulin,and gluten was the largest.The content of protein and protein components in grain and flour were not affected by foliar Zn spraying.However,in terms of Zn₁,the increase of gluten content in grain and flour was higher than that under the condition of Zn₀ with the increase of N dosage,which was 37.5%and 38.1%,respectively.In conclusion,although continuous application of Zn fertilizer on calcareous soil can greatly increase the effective Zn content,the effect of grain Zn enrichment is limited,which is far from reaching the goal of Zn enrichment.However,foliar spraying of Zn could significantly increase the grain Zn content and achieve the goal of grain Zn enrichment,which was independent of the available Zn content in soil.The combination of foliar spraying and soil application of Zn could not only achieve the expected target of Zn enrichment,but also improve the protein pool of Zn storage in the whole grain and flour,indicating that this measure could simultaneously improve the nutritional quality of Zn and N in wheat grains.These conclusions can provide important scientific and practical basis for wheat grain Zn nutritional quality improvement on calcareous soil in northern China.