To alleviate human zinc (Zn) deficiency, it is worthy to develop rational agronomic managements to achieve high yielding and high resource-use efficiency wheat (Triticum aestivum L.) grains biofortified with Zn. Effects of application of three rates of nitrogen (N) fertilizer (75,200 and 275 kg·ha−1) to soil in combination with three foliar applications (deionized water, Zn alone, and a combination of Zn and sucrose) on grain yield, yield components, grain Zn concentration, protein, phytic acid (PA), phosphorus (P), calcium (Ca), and carbon (C), as well as on Zn bioavailability, were investigated in four wheat cultivars (“Jinan 17,” “Jimai 20,” “Jimai 22,” and “Luyuan 502”) under field conditions. Enhanced N increased Zn and protein concentrations as well as bioavailability; excessive N input did not result in further improvements. Zinc spraying was more effective than soil fertilizer N application, the spray of Zn (with or without sucrose) increased grain Zn concentrations by 11.1–15.6 mg·kg−1 (27.1–38.1%), and increased grain Zn bioavailability, estimated using total daily absorbed Zn (TAZ) and molar ratios of PA/Zn) and PA × Ca/Zn, by 0.4–0.6 mg d−1 (28.6–42.9%), 23.1–27.4% and 24.0–28.0%, respectively. Remarkably, increases caused by ‘Zn + sucrose’ were higher than spraying Zn alone. Grain Zn bioavailability was more sensitive to the selection of cultivar than Zn concentrations. Among cultivars, the higher the grain yields and concentrations of antinutritional compounds, the lower the grain Zn nutritional quality would be. 200 kg N ha−1 application rate in combination with foliar spraying of “Zn + sucrose” maximized grain Zn concentrations of “Jinan 17,” “Jimai 20,” “Jimai 22,” and “Luyuan 502” to be 59.4, 56.9, 55.8, and 60.9 mg kg−1, respectively, achieving the target value for biofortification. Additionally, PA/Zn and PA × Ca/Zn of “Jinan 17,” “Jimai 20,” and “Luyuan 502” were <15 and 200, and TAZ was maximized to be 2.2, 2.0, and 2.1 mg d−1, respectively, indicating higher bioavailability. Therefore, optimal soil N and foliar Zn management together with suitable cultivars maintained high grain yield with lower N input and could substantially increase grain Zn nutritional quality simultaneously.

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Agronomy practices aimed at wheat (Triticum aestivum L.) grain Zn biofortification are important to alleviate Zn deficiency in humans, especially for those resource-poor people owing to subsistence on diets dominated by cereal-based foods with low concentrations and bioavailability of Zn. To promote understanding of source-sink flow processes affecting biofortification of wheat with Zn, effects of different source/sink manipulations on grain Zn accumulation by wheat were examined in pot and field at two locations. Treatments included foliar applications of deionized water, sucrose, ZnSO4, sucrose + Zn, defoliation, spike shading or partial removal of spikes. Results showed sucrose + Zn significantly increased grain Zn concentration more than Zn alone. Grain Zn concentration with sucrose + Zn averaged 66 mg kg -1 for 'Kenong 9204' and 59 mg kg -1 for 'Liangxing 99' in pot, and ranged from 42 to 58 mg kg -1 for 'Liangxing 99', 'Jinan 17', 'Jimai 20', 'Jimai 22', and 'Luyuan 502' under field, approaching the field-grown target 60 mg kg -1 proposed by World Health Organization. Molar ratios of phytic acid/Zn and phytic acid × Ca/Zn of 'Jinan 17', 'Jimai 20' or 'Luyuan 502' with sucrose + Zn were reduced to be < 15 and < 200, respectively, suggesting higher Zn bioavailability. Defoliation or spike shading decreased grain weight, Zn concentration and content. It is concluded that grain Zn accumulation of wheat can be affected by the sourcesink relationship of Zn and/or carbohydrate, and the foliar spray 'sucrose + Zn' is recommended for increasing concentration and bioavailability of Zn in wheat grains.

No abstract

Zinc (Zn) deficiency is a global nutritional problem that is reduced through agronomic biofortification. In the current study, the effects of foliar spraying of exogenous ZnSO 4 ·7H 2 O (0.2% in Quzhou and 0.3% in Licheng, w/v) and/or sucrose (10.0%, w/v) on maize (Zea mays L.) agronomic traits; concentrations of Zn, iron (Fe), calcium (Ca), total phosphorus (P), phytic acid (PA) P, carbon (C), and nitrogen (N); C/N ratios; and Zn and Fe bioavailability (as evaluated by molar ratios of PA/Zn, PA × Ca/Zn, PA/Fe and PA × Ca/Fe) in maize grains were studied under field conditions for two years at two experimental locations. The results confirmed that there were no significant differences in maize agronomic traits following the various foliar treatments. Compared with the control treatment of foliar spraying with deionized water, foliar applications of Zn alone or combined with sucrose significantly increased maize grain Zn concentrations by 29.2-58.3% in Quzhou (from 18.4-19.9 to 25.2-29.6 mg/kg) and by 39.8-47.8% in Licheng (from 24.9 to 34.8-36.8 mg/kg), as well as its bioavailability. No significant differences were found between the foliar spraying of deionized water and sucrose, and between Zn-only and "sucrose + Zn" at each N application rate and across different N application rates and experimental sites. Similar results were observed for maize grain Fe concentrations and bioavailability, but the Fe concentration increased to a smaller extent than Zn. Foliar Zn spraying alone or with sucrose increased maize grain Fe concentrations by 4.7-28.4% in Quzhou (from 13.4-17.1 to 15.2-18.5 mg/kg) and by 15.4-25.0% in Licheng (from 24.0 to 27.7-30.0 mg/kg). Iron concentrations were significantly and positively correlated with Zn at each N application rate and across different N application rates and experimental locations, indicating that foliar Zn spraying facilitated the transport of endogenous Fe to maize grains. Therefore, foliar Zn spraying increased the Zn concentration and bioavailability in maize grains irrespective of foliar sucrose supply while also improving Fe concentrations and bioavailability to some extent. This is a promising agricultural practice for simultaneous Zn and Fe biofortification in maize grains, i.e., "killing two birds with one stone".