Global Dataset of Rare Metal Ion Concentrations in Wheat-Growing Region Soils

Field sampling campaigns were conducted across 160 paired farmland plots and their adjacent natural ecosystems in 31 countries spanning six continents (Figure 1b). Each farmland site was spatially paired with a natural ecosystem within approximately one kilometer to ensure comparable climatic and edaphic conditions, with natural sites serving as relatively undisturbed reference systems. Surface soil samples were collected between April 2023 and September 2024. Within each paired location, a 20 m × 20 m plot was established on both farmland and the corresponding natural ecosystem. Each plot’s four corners contained 1 m × 1 m subplots. From each subplot, five surface soil samples (0-20 cm depth) were randomly collected and thoroughly combined to form a composite sample. Four composite samples were collected independently from each farmland and its corresponding natural ecosystem at each site, resulting in a dataset comprising 1280 soil samples across all locations. Sampling at paired plots was conducted on the same day to minimize temporal variation. Surface soil layers were specifically targeted, given their high sensitivity to land-use changes. Samples were transported under cooled conditions to the laboratory, where they were air-dried before subsequent analyses. This dataset contains raw test data for four rare metal elements: Ba, Bi, V, and Li.