Chemical speciation of zinc in fertilized neutral soils governs zinc mobility and phytoavailability

Abstract Applied Zn undergoes multiple biogeochemical reactions that determine the available Zn concentration in soil. The choice of Zn fertilizer should depend on the chemical reactions it undergoes, namely, adsorption‐desorption, precipitation‐dissolution, and complexation‐dissociation. The treatments included four different Zn fertilizers: ZnO, ZnSO 4 .7H 2 O (ZnSO 4 ), ZnEDTA, and Zn mix (a new Zn product with 60% ZnO, 36% ZnSO 4 ·7H 2 O, and 4% ZnEDTA by weight). The treatments also included a control (No‐Zn) and an ethylenediamine tetraacetic acid (EDTA) treatment (No‐Zn + EDTA). The overall objective of this study was to compare the above treatments based on relative Zn diffusion, water extractability, plant biomass, and plant Zn uptake using incubation (soil only) and greenhouse (soil + plant) studies. The X‐ray absorption near‐edge structure (XANES) spectroscopy was used to evaluate the Zn reaction products in soil. Zinc sulfate and ZnEDTA showed greater diffusion, water extractability, plant concentration, and diethylenetriaminepentaacetic acid extractability of Zn in soil than ZnO and Zn mix treatments. The XANES analysis showed that Zn mainly existed as Zn aluminum nitrate double‐layered hydroxide (ZnALDHnitrate)‐like species in all treatments except ZnEDTA, complementing our understanding from the incubation and greenhouse studies that Zn gets sorbed quickly to metal oxides or soil surfaces. Plant uptake, Zn concentration, and biomass were comparable between ZnSO 4 and ZnEDTA, indicating that both can serve as effective Zn sources under neutral soil conditions. Given its comparable performance and lower cost, ZnSO 4 represents a practical alternative to chelated Zn sources such as ZnEDTA.