Environmental implications of land use change on the fate of Zn in agricultural soils: A case study of Puding karst soils, southwest China

Land use change threatens food security because it may cause the depletion and/or low bioavailability of micronutrients in agricultural soils. Therefore, it is significant to investigate the fate of micronutrients and predict the potential environmental problems. The zinc isotope technique is of particular interest in interpreting soil processes. In this study, Zn isotopic data of soil samples in five profiles based on different land uses were provided, and Zn behavior in different soils was discussed. The isotopic ratios of soil samples in the abandoned orchard, secondary forest, abandoned cropland, and cropland are similar, with the δ66Zn varying from 0.15 to 0.29‰. However, the samples in shrub grassland show a lower δ66Zn of 0–0.20‰, which may be affected by anthropogenic sources. For the vertical patterns, the non-cultivated long-rooted plants (i.e., abandoned orchard and secondary forest) show no significant difference in the distribution of δ66Zn, but the patterns of cropland and abandoned cropland samples are reversed. The cropland samples show positive correlations between δ66Zn and Fe2O3 (R2 = 0.90) and MnO (R2 = 0.75), indicating that Fe and Mn oxides preferentially adsorb heavy Zn isotopes on the mineral surfaces. The high affinity between Zn and oxides indicated that the concentration of bio-available Zn in cropland soils was getting lower. As a result, the supplies of micronutrients may be deficient and urged from fertilizer. This study provides a better understanding of Zn cycling in agricultural systems and gives improvements in soil management.