Abstract:
Objectives Understanding the response of pre- and post-anthesis Zn uptake and translocation in wheat to Zn fertilizer input and grain Zn concentration and their relationships with soil Zn fractions and its availability is of great importance to achieve grain Zn biofortification in drylands, particularly in the Loess Plateau where Zn is deficient in wheat grain.
Methods Based on the location-fixed field experiment initiated in 2017 on dryland of the Loess Plateau, soil Zn fractions and availability, pre- and post-anthesis Zn uptake and transportation and grain Zn concentrations of wheat were analyzed under different Zn application rates in the cropping seasons of 2021−2022 and 2022−2023.
Results Results showed that Zn application did not significantly affect the grain yield, but the grain Zn concentration was increased by 44.7% and 38.2% in two seasons, with the highest of 33.6 mg/kg at 25.6 kg Zn hm2. Correspondingly, pre-anthesis Zn uptake was increased respectively by 38.8%−83.7% and 13.4%−49.0% in that two seasons, post-anthesis Zn translocation was increased by 36.0%−73.9% and 13.0%−39.6%; while effects of Zn application on post-anthesis Zn uptake changed with years. Soil available Zn was increased by 11.6 and 11.3-fold respectively in the top soil of 0−20 and 20−40 cm, with the highest available Zn concentrations of 9.20 and 3.57 mg/kg. Correspondingly, the increases of 4.4, 1.8, and 1.9-fold respectively in the deep soil of 40−60, 60−80, and 80−100 cm, with the highest available Zn concentrations of 0.54, 0.28, and 0.29 mg/kg. Zinc fractions also significantly changed with Zn application. Water-soluble Zn was increased by 54.5% and 75.0% and maximized to 0.17 and 0.14 mg/kg, Zn weakly bound to organic matter was increased by 214.9% and 90.8% and maximized to 5.70 and 3.11 mg/kg, carbonate bound Zn was increased by 1178.0% and 551.7% and maximized to 5.24 and 1.89 mg/kg, manganese oxide bound Zn was increased by 345.9% and 183.9% and maximized to 15.52 and 9.37 mg/kg, Zn strongly bound to organic matter was increased by 91.5% and 34.4% and maximized to 1.13 and 0.86 mg/kg, and residue mineral Zn was increased by 23.7% and 24.3% and maximized to 56.57 and 56.80 mg/kg in the layer soil of 0−20 and 20−40 cm, respectively.
Conclusions Zn fertilizer application not only increased the concentration of Zn weakly bound to organic matter, carbonate bound Zn and manganese oxide bound Zn in soil but also promoted their transformation into a higher available fraction as water-soluble Zn, and this consequently could sustain the available Zn pool in top soil. The enhanced soil available Zn supply could increase wheat grain Zn concentration due to the promoted pre-anthesis Zn uptake and its transfer of Zn from shoot to grain post-anthesis, while the post-anthesis Zn uptake was inhibited by the inherent drought in dryland, the further grain Zn fortification with Zn fertilizer application was limited for wheat grown on the Loess Plateau.
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