硫酸锌和EDTA-Zn不同施用方法对第二季小麦籽粒锌和土壤锌有效性的影响

【目的】在潜在缺锌石灰性土壤上，特别是种植小麦并以此为主粮的地区，缺锌问题日益受到人们的关注。提高小麦籽粒锌含量以满足人体锌需求，对于改善人体锌营养不良的现状具有重要意义。【方法】以ZnSO₄和Zn-EDTA为锌源，布置了2个为期两年的田间定位试验。试验均采用裂区设计，即主因子为喷施锌肥，设喷施与不喷2个主处理；副因子为土施方法，设不施锌、均施、条施3个副处理。在第1季试验基础上，第2季不再土施锌肥，调查了小麦籽粒锌含量、土壤有效锌含量及锌组分含量，分析了第1季锌肥的后效。【结果】第2季单独喷施ZnSO₄小麦籽粒Zn含量提高了11.13 mg/kg，提高幅度为33%，而喷Zn-EDTA无明显效果。不喷Zn时，第1季均施和条施的ZnSO₄在第2季均表现出一定后效，小麦籽粒锌含量比对照分别提高了6.05、3.51 mg/kg，提高幅度为20%和11%；喷Zn时，第2季均施和条施ZnSO₄处理的小麦籽粒锌含量增加了28.59和21.59 mg/kg，增幅100%和76%，表现出显著富锌作用，但增加幅度比单独喷施要小很多。第1季土施的两种锌肥在第2季小麦收获后DTPA-Zn仍维持在1 mg/kg以上，即不喷Zn时，均施和条施ZnSO₄处理的土壤有效锌含量分别为1.99和1.65 mg/kg，均施和条施Zn-EDTA的有效锌含量分别为1.23和1.01 mg/kg；喷Zn时，均施和条施ZnSO₄处理的土壤有效锌含量分别为1.44和2.22 mg/kg，均施和条施Zn-EDTA处理的有效锌含量分别为1.16和1.10 mg/kg。土壤各锌组分含量均表现为:松结有机态Zn > 碳酸盐结合态Zn > 氧化锰结合态Zn > 紧结有机态Zn > 交换态Zn。具体而言，第1季均施和条施ZnSO₄，第2季结束后交换态Zn（Ex-Zn）、松结有机态Zn（Wbo-Zn）、碳酸盐结合态Zn（Car-Zn）含量均显著提高，其提高幅度分别为184%和116%；75%和85%；53%和43%。而均施和条施Zn-EDTA仅Ex-Zn、Wbo-Zn含量显著提高，其提高幅度分别为232%和132%；18%和10%。均施Zn-EDTA处理的锌肥利用率为0.27%，条施为0.70%，后者约为前者的3倍；而条施与均施ZnSO₄无差异。【结论】在潜在缺锌石灰性土壤上，单独喷施ZnSO₄显著提高了小麦籽粒锌含量，而喷施Zn-EDTA效果不显著；土施ZnSO₄和Zn-EDTA，不论条施或均施，虽然会使有效锌（DTPA-Zn）及较高活性锌形态（Ex-Zn、Wbo-Zn）长时间维持较高含量，但对第2季小麦籽粒富锌的后效有限；土施基础上配合喷施ZnSO₄对小麦籽粒锌的含量效果最令人满意。

Effects of different application method of ZnSO4 and EDTA-Zn on wheat grain zinc biofortification and soil zinc availability in the next year

Objectives]Human Zn deficiency has been concerned in potentially Zn deficient soil, especially in areas where wheat is the staple food. Increasing Zn concentration in wheat grain to meet human Zn requirement is critical for alleviating human Zn deficiency.Methods]A two-year field experiment with the split block design was conducted using ZnSO4 and Zn-EDTA as Zn sources. The main factor was Zn application methods, which included foliar application and soil application, and the soil application was splited into mixed and banded application methods during the first cropping year. Only foliar Zn application was conducted during the second cropping year. All data in this paper were collected in the second cropping year.Result]In the second season when Zn was foliar applied, the grain Zn concentration was significantly increased by 11.13 mg/kg (33%) by foliar spray of ZnSO4 alone, not by foliar Zn-EDTA application. Without foliar Zn application, the grain Zn contents were increased by 6.05 and 3.51 mg/kg (20% and 11%) under the mixed and banding ZnSO4 fertilization, compared with the no Zn treatment in the second cropping year, respectively. With the foliar Zn application, the wheat grain Zn contents were increased by 28.59 mg/kg (100%) and 21.59 mg/kg (76%) under the mixed and banding ZnSO4 fertilization, but these increases were much less than those of applying foliar Zn alone. Soil DTPA-Zn after wheat harvest in the second cropping year maintained above 1 mg/kg when Zn fertilizer was added to soil at the first season. Specifically, soil DTPA-Zn contents were respectively 1.99 and 1.65 mg/kg under the mixed and banding ZnSO4, while the contents were respectively 1.23 and 1.01 mg/kg under the mixed and banding Zn-EDTA fertilization. Under condition of the foliar Zn fertilization, the contents of DTPA-Zn were 1.44 and 2.22 mg/kg respectively under mixed and banding ZnSO4 fertilization, and 1.16 and 1.10 mg/kg respectively under the mixed and banding Zn-EDTA fertilization. The contents of soil Zn fractions were in the order of:weakly bounded organic matter Zn (Wbo-Zn) > carbonate bound Zn (Car-Zn) > manganese oxides bound (MnO-Zn) > tightly bounded organic Zn (Tom-Zn) > exchangeable Zn (Ex-Zn). Specifically, the contents of Ex-Zn, Wbo-Zn, and Car-Zn were significantly increased by 184%, 75% and 53%, respectively with mixed ZnSO4, while the increases were respectively 116%, 85%, and 43% with banding ZnSO4. However, only the Ex-Zn and Wbo-Zn were increased under the mixed and banding Zn-EDTA, and the increases relative to the mixed Zn-EDTA were respectively 232% and 18%, while the increases were 132% and 10% respectively in the treatment of banding Zn-EDTA. Compared with the non Zn treatment, the Zn use efficiency in the mixed Zn-EDTA fertilization treatment was 0.27%, while in the banding treatment, the efficiency was 0.70%, which was three times higher than that of the mixed one. No differences were observed between the mixed and banding ZnSO4.Conclusion]Foliar application of ZnSO4 alone can significanlty increase grain Zn concentration of wheat grown on potentially Zn-deficient soil, while foliar Zn-EDTA has little effect. Although it can lead to high level of soil DTPA-Zn and Zn fractions with higher mobility (Ex-Zn, Wbo-Zn), mixed or banded Zn-EDTA and ZnSO4 has little effect on grain Zn concentration in the next cropping year. Soil application combined with foliar spray of ZnSO4 is satisfactory in increasing Zn concentration in wheat grain.