Field-scale studies quantify limitations for wheat grain zinc biofortification in dryland areas

Optimizing of agronomic measures is an efficient way to improve crop zinc (Zn) nutrition and human dietary Zn intake. We collected field management, soil, and plant information from 78 fields in Shuiqing, 106 fields in Yongshou, and 120 fields in Qiujialing on China's Loess Plateau to explore limitations in wheat grain Zn and design alternative options to achieve the target grain Zn concentration (40 mg kg-1). The Shuiqing fields had an average grain yield of 5022 kg ha-1 and grain Zn concentration of 22.8 mg kg-1, with no fields achieving the target grain Zn concentration due to phosphorus (P) fertilizer overuse (254 kg P2O5 ha-1) and very low soil DTPA-Zn (0.23 mg kg-1). Two Yongshou fields reached the target grain Zn concentration but had 52.3%, 16.0%, and 51.4% lower average grain yield, P fertilizer rate, and soil Olsen-P, respectively, than other fields. The Qiujialing fields had an average grain Zn concentration of 34.8 mg kg-1, with 18.3% of fields >= 40 mg kg-1, of which 91% had soil DTPA-Zn >= 0.5 mg kg-1 and 45.2% higher grain Zn uptake than other fields due to newly released wheat cultivars, low P fertilizer rates, low soil Olsen-P, and high soil mineral nitrogen. In conclusion, a feasible framework for achieving the target grain Zn level would be using cultivars with high Zn uptake capacity, reducing P fertilizer use and soil Olsen-P, and improving soil available Zn in low Zn soils.