Spatio-Temporal Variability and the Factors Influencing Soil-Available Heavy Metal Micronutrients in Different Agricultural Sub-Catchments

Information on the spatial variability of soil-available micronutrients is important for farming and soil management practices. As current knowledge of factors influencing soil available micro-nutrients in the long-term scales is limited, we analyzed 821 and 812 representative surface (0–20 cm) soil samples from five sub-catchments in the Ping Gu intermontane basin in Beijing, China in 2007 and 2017. The objectives of this study were to assess the temporal and spatial distribution characteristics of soil-available micronutrients (Cu, Zn, Fe and Mn) and their relationships with soil’s chemical properties. The concentration of available Cu ranged from 1–2 mg∙kg −1 distributing over a large area in 2007, but it was more than 2 mg∙kg −1 in the hilly regions in 2017. The concentration of available Zn (>5 mg∙kg −1 ) increased significantly from 2007 to 2017, and showed an uneven distribution. The distribution of available Fe and Mn decreased from the northeast to the southwest region of the study area between 2007 and 2017, this being consistent with the topography in this area. Soil’s available P (AP) had a higher contribution to available Cu and Zn in different sub-catchments. In addition, soil pH had a significant negative influence on available Fe in sub-catchments 1, 2 and 3, and on available Mn in all sub-catchments, except for sub-catchment 4. Moreover, the effects of soil chemical properties on soil-available micronutrients increased in each sub-catchment from 2007 to 2017. We conclude that differences in soil properties and land-use types were the main reasons for the spatial variability of soil-available micronutrients in the Ping Gu intermontane basin.