Objectives The effects of different fertilization treatments on soil total and available iron (Fe), manganese (Mn), zinc (Zn), copper (Cu) contents, as well as the absorption of Fe, Mn, Zn, Cu by wheat were investigated, aiming to provide a theoretical basis for the improvement of farmland fertility and high yield and good quality of crops in fluvo-aquic soil area of North China Plain.

Methods The long-term fertilization experiment, located in Zhengzhou, Henan Province, had lasted 31 years, and the cropping system was winter wheat and summer maize rotation. Five fertilization treatments were included: no fertilization (CK), nitrogen and potash fertilizer (NK), nitrogen, phosphorous and potash fertilizer (NPK), NPK combined with maize straw (NPKS), NPK combined with organic manure (NPKM). The contents of total and available Fe, Mn, Zn, and Cu were analyzed using the soil samples collected since the beginning, and the micronutrient contents of wheat grains and straw in 2019 and 2021 were analyzed.

Results After 31 years of fertilization, the soil total Fe and Mn contents under all the treatments were not significantly different from those at the beginning. Comparing with the initial value, the soil total Zn and Cu contents increased significantly; NPKM treatment was measured the highest soil total Fe, Mn, Zn and Cu contents. Compared with CK treatment, NPK, NPKS, and NPKM treatments significantly increased soil organic matter and cation exchange capacity, reduced soil pH, which was conducive to the transformation of soil trace elements into available forms. NPKM and NPKS treatments were tested relatively higher soil available Fe, Mn, and Zn contents. And NPK treatment was measured 52% and 49% higher available Fe, and 39% and 11% higher available Mn than CK and NK treatments, respectively. Compared with CK and NK treatment, NPKM, NPKS, and NPK treatments significantly increased trace elements uptake in wheat shoots and the trace elements harvest index, but decreased grain trace element content as the dilution effect of grain yields, the Fe and Zn contents in grains under NPK, NPKS, and NPKM treatments were 71%−74% and 60%−63% of the recommended lower limit, respectively.

Conclusions The application of chemical fertilizer combined with straw or organic fertilizer is beneficial to the availability of Fe, Mn, Zn, and Cu, thereby increased the uptake of trace elements by wheat. Even though, the combined application of chemical and organic fertilizers leads to decreased micronutrient contents because of the dilution effect of yield. Therefore, optimized agronomic management practices should be considered for keeping the nutritional quality as well as the yield in fluvo-aquic soil area.