Fate and Plant Uptake of Different Zinc Fertilizer Sources upon Their Application to an Alkaline Calcareous Soil

To effectively manage soil for optimum crop production, it is crucial to understand how zinc (Zn) interacts and speciates in Zn-deficient calcareous soils. This study employed incubation-visualization and short-term (5 weeks) greenhouse studies to evaluate fate, transport, and extractability of Zn in soil and Zn plant uptake. Further X-ray absorption near-edge structure (XANES) spectroscopy was employed to identify the chemical species of Zn in Zn-coated urea-treated soils. The objectives were to compare the efficiency and investigate the reaction products and pathways of Zn-only sources and Zn-coated urea sources in a calcareous soil. Out of Zn-only treatments, plant biomass was significantly higher for ZnO (0.62 g) and Zn mix (60% ZnO plus ZnSO4 and Zn-EDTA) (0.71 g) than the no-Zn control (0.4 g), ZnSO4 (0.5 g), and ZnP (0.5 g). Meanwhile, Zn diffusion and extractability were greatest for ZnEDTA, and this was supported by soil solution Zn results, which indicated that the solution Zn concentration in ZnEDTA was on an average 13 times greater than all other Zn-only treatments and the control. Zinc-coated urea sources provided more soluble and plant-available Zn, likely due to the enhanced solubility facilitated by urea. Synchrotron-based XANES results were in agreement and confirmed various resulting reaction products for Zn-coated urea products. Our results showed that, in calcareous soils, high solubility might not be the only indicator to test Zn fertilizer use efficiency; less soluble sources behave as efficiently as highly soluble sources due to their ability to reduce sorption reactions limiting Zn availability.