Influence of ZnO Particle Size and Soil Characteristics on the Estimation of Long-Term Zn Bioavailability by Chemical Extraction Methods and Diffusive Gradients in Thin-Films (DGT)

The aim of this paper is to explore whether the long-term bioavailability of Zn in different soils can be predicted using operational extraction procedures. Green peas and beetroot were grown in two soils with contrasting physicochemical characteristics. Two Zn sources of different sizes (ZnO-nano or ZnO-bulk) were applied 1 year earlier, at different Zn application rates. The amounts of available Zn were assessed using the diffusive gradients in thin films (DGT) technique and different chemical extraction procedures: water-soluble (WS), CaCl 2 , rhizosphere-based low-molecular-weight organic acid (LMWOAs), DTPA-TEA, and NH 4 Ac. The different correlation and regression studies showed that the estimation of availability is dependent on the soil categorical variable, especially in the beetroot crop. Zn-DGT could be used to estimate the Zn concentration of the aerial part of the green pea using a general model for both soil and ZnO sizes. The estimation of long-term Zn bioavailability was successful using either medium-strength extractive solutions or the DGT technique. The extraction methods involving complexing agents or buffered salt solution overestimated the amount of bioavailable Zn in calcareous soil. Further studies will be necessary to know the amounts of Zn associated with the different soil fractions. Graphical abstract