Effects Of Zinc Fertilizer Application On Zn Diffusion-transformation-uptake Of Wheat Plants On Potentially Zn Deficient Calcareous Soil

As the main food crops for northern Chinese, wheat is mainly grown on potentially Zn-deficient calcareous soils. Wheat grain Zn concentration is mainly 20³0 mg·kg-1 and people are usually Zn deficient. To increase wheat grain Zn concentration and solve Zn deficiency, the most directly and efficiently method is to increase soil DTPA-Zn concentration, which can be increased by Zn fertilization. However, the previous field experiments indiciated that Zn applicationt to calcareous soil had no significant effect on increasing grain Zn concentration, and even increasing the application rate. Should grain Zn concentration being increased by soil or foliar application of chelated Zn fertilizer or localized application methods? How to increase the effenciency of Zn fertilizer, it is very important to research the diffusion and transformation of Zn after Zn fertilier applide to this potentially Zn deficient calcareous soil. Meanwhile, studies on the effect of Zn-EDTA on grain Zn concentration of wheat on potentially Zn-deficient soil are little and the transformation and fractions of chelated Zn ferilizer applied to this calcareous soil is unknown. Therefore, two field experiments on potentially Zn-deficient soil and three greenhouse experiments were conducted to study the effects of Zn fertilization with different application methods and Zn sources on grain Zn nutritional quality of winter wheat and Zn transformation in soil. Main results were as follows:1. To compare the effect of soil and foliar applicatoin of ZnSO₄ on grain Zn nutritional quality of five wheat cultivars, a two-year fied experiment will be carried out. Results showed that soil Zn application increased soil DTPA-Zn by an average of 174%, but had a little effect effect on grain Zn concentration. In contrast, foliar Zn application increased grain Zn concentration by an average of 61%, and Zn bioavailability by an average of 36%. Soil DTPA-Zn concentrations varied depending on wheat cultivars. There were also significant differences in grain phytic acid concentration among the cultivars. Compared to soil Zn application, foliar Zn application is more effective in improving grain Zn content of wheat grown in potentially Zn-deficient calcareous soils.2. To study the diffusion mechnism of ZnSO₄（20 mg Zn·kg-1） and Zn-EDTA（4 mg Zn·kg-1） applied to soil by 5-mm wide space and 1-mm-wide space, a laboratory experiment was carried out. Results from the diffusion experiment showed that both the extractability and the diffusion coefficient of Zn were higher when Zn fertilizer was applied in a 1-mm-wide space than when it was applied in a 5-mm-wide space. Even when Zn-EDTA was applied only one-fifth the rate of ZnSO₄, Zn-EDTA had a greater diffusion distance than ZnSO₄. Based on the reslts of the diffusion experiment, to compare the effects of the two Zn fertilizers and two application methods on grain Zn concentration, a greenhouse pot experiment was carried out. The greenhouse experiment showed that the mixed ZnSO₄ application and Zn-EDTA application（either in the mixed or banded application） treatments significantly increased the concentration and bio-accessibility of Zn in wheat grain. The effect of Zn-EDTA in all case on Zn concentration and bio-accessibility in wheat grain was greater than that of ZnSO₄. The banded application reduced the effectiveness of ZnSO₄, not for Zn-EDTA.3. A greenhouse pot experiment to compare the effects of ZnSO₄ and Zn-EDTA on Zn fractions. Results showed that the manganese oxide bound Zn（OxMn-Zn） fraction played a major role in soil DTPA-Zn in the banded ZnSO₄ application; however, the tight organic matter bound Zn（TOM-Zn） fraction had a significant influence on soil DTPA-Zn in the mixed ZnSO₄ application. Despite the application method, Zn-EDTA applied to soil increased the concentrations of exchangeable Zn（Ex-Zn）, carbonate bound Zn（Carb-Zn）, and loose organic matter bound Zn（LOM-Zn）. The Ex-Zn and LOM-Zn influenced the soil DTPA-Zn concentrations in the mixed and banded Zn-EDTA application methods. Furthermore, Ex-Zn and LOM-Zn were distributed uniformly in the application zone and the non-application zone in the banded Zn-EDTA application. In conclusion, Zn-EDTA contributes a higher amount of active Zn fractions（Ex-Zn and LOM-Zn） in calcareous soil and is more effective at increasing the wheat-grain Zn concentration compared with ZnSO₄.4. The objective of this study was to compare the efficiency of ZnSO₄ and Zn-EDTA. The two Zn fertilizer sources were applied mixed and banded with the soil. A calcareous soil with low available Zn was used. Zn rates were 10, 20 mg Zn·kg-1 soil for ZnSO₄ and 4, 10, 20 mg Zn·kg-1 soil for Zn-EDTA. Results showed that the mixed ZnSO₄ application and Zn-EDTA application（either in the mixed or banded application） treatments significantly increased the concentration and bioavailability of Zn in wheat grain. Zinc concentration and bioavailability of wheat grain was significantly increased with increasing Zn-EDTA apply rate. The effect of Zn-EDTA in all case on Zn concentration and bioavailability in wheat grain was greater than that of ZnSO₄. The banded application treatment reduced the efficiency of Zn SO₄, not for Zn-EDTA. Zinc application had a little effect on phytic acid concentration in wheat grain. However, the estimated Zn bioavailability was lower than 3 mg. In conclusion, the high phytic acid concentration and the [phytic acid]/[Zn] ratio in wheat grain attributed to low estimated Zn bioavailability. To meet Zn requirement for the human population groups reliant on wheat grains, grain phytic acid concentration was needed further reduced.5. A field experiment was carried out to compare the effect of soil and foliar application of ZnSO₄ and Zn-EDTA on grain Zn nutritional quality in calcareous soil. Results showed that soil application of ZnSO₄ or Zn-EDTA had significant little effect on wheat grain Zn concentrations. Foliar application+soil application of ZnSO₄（in mixed and banded application method） significantly increased grain Zn concentration by 67.2%; reduced phytic acid concentration by 67.3%, reduced [phytic acid]/[Zn] ratio by 41.9% and finally increased grain Zn bioavailability by 48.4%. On the other hand, foliar application+soil application of Zn-EDTA had no remarkable effect on wheat grain Zn concentrations and grain Zn concentration was increased by 12.0% compared to the control. The foliar application+soil application of Zn-EDTA reduced [phytic acid]/[Zn] ratio by 14.8% and grain Zn bioavailability was increased by 18.1%. Compared to the banded Zn application treatment, the mixed application treatments remarkably increased grain Zn bioavailability. The effect of ZnSO₄ on increasing grain Zn bioavailability was greater than Zn-EDTA.6. A field experiment was conducted to compare the effect of two Zn sources（ZnEDTA and ZnSO₄） and two application methods（mix and band） on the concentrations of Zn fractions and DTPA-Zn. Results showed that the banded Zn fertilizer（ZnEDTA or ZnSO₄） application methods remarkably increased soil DTPA-Zn and Zn fractions concentrations in the planting row. The order of Zn fractions decreased as follows: LOM-Zn > Carb-Zn > TOM-Zn > OxMn-Zn > Ex-Zn. Compared to the mixed ZnSO₄ and Zn-EDTA treatments, the banded ZnSO₄ and Zn-EDTA increased soil DTPA-Zn in the planting row and un-planting row by 1.77 and 1.69 times, respectively. Soil DTPA-Zn positively correlated with Ex-Zn, LOM-Zn, and Carb-Zn. Compared to the control, soil Ex-Zn concentration was significantly increased in the Zn-EDTA application treatments. Otherwise, soil Ex-Zn concentration was significantly higher in the banded Zn-EDTA treatment than that in the mixed treatment.Based on the results of 1 simulated experiment, 3 greenhouse experiment and 1 field experiment, conlusions can be made:（1） Zn fertilizer applied to potentially Zn-deficient calcareous soil can remarkably increase soil DTPA-Zn concentration; however, soil Zn application had no significant effect on grain Zn concentrations. A high rate of Zn-EDTA application and folair ZnSO₄ application can significantly increase grain Zn concentration; however, foliar application of Zn-EDTA had no significant effect on grain Zn concentration.（2） Compared to ZnSO₄, the application of Zn-EDTA had a higher diffusion rate, and the Ex-Zn and LOM-Zn concentrations were also higher; otherwise, in the application of Zn-EDTA treatment, Ex-Zn, LOM-Zn and Carb-Zn had a remarkable relationship with soil DTPA-Zn.（3） Comparison of mixed application of ZnSO₄, in the banded ZnSO₄ application, soil DTPA-Zn was mainly restricted in the fertilized-section, which reduced the contact chances between Zn fertilizer granuler and the wheat roots and OxMn-Zn significantly correlated with soil DTPA-Zn, finally the fertilizer utilization was reduced. Therefore, on potentially Zn-deficient calcareous soil, soil application of Zn-EDTA and foliar application of ZnSO₄ or containing higher Ex-Zn and LOM-Zn concentration can increase grain Zn concentration.