Micronutrients in Amazonian Dark Earths and Adjacent Soils

The present dataset is the result of a literature review but also contains original field data obtained by the authors in Amazonian Dark Earths (ADE) and Adjacent soils (ADJ) at nine paired sites. The main objective of this study was to assess the effect of ADEs on micronutrient contents (Ni, Cu, Mn, Zn, Fe and B), compared with ADJ soils, and the impacts of land use.
Studies including peer-reviewed papers, dissertations and theses that evaluated extractable/exchangeable, pseudo-total, total and oxide micronutrient contents in ADEs and ADJ soils published between 1988 and 2020 were searched in online databases, including Science Direct, Web of Science, Google Scholar, Scielo, and the Brazilian Digital Library of Theses and Dissertations (Biblioteca Digital de Teses e Dissertação, BDTD). Besides the present field study (authors' data), we found 20 other studies that fitted our selection criteria for this review: i.e., the studies must have measured micronutrient contents in comparable depth increments and soil types in both ADEs and ADJ soils nearby or next to the ADE, and the values reported must have been greater than 0, in order to permit calculation of the “ADE-effect” (see below). Only seven studies besides the current study reported extractable micronutrient contents measured with Mehlich-1, while the remaining studies reported total, pseudo-total or “oxide” contents, or measured extractable micronutrients using different methods. Extractable contents refer to those obtained with Mehlich-1 or resin, pseudo-total contents those including extraction using HNO3 with or without HCl or H2O2, total contents any study involving HF with other extractors, and oxide contents those involving sodium dithionite-citrate-bicarbonate or X-ray fluorescence (semi-quantitative method).
Data extracted from these publications included four soil variables (horizon, sample depth, soil type and micronutrient concentrations), four biogeographic variables (vegetation cover/land use, location, county and state) and two methodological variables, i.e., micronutrients analyzed and extraction method. When the data was presented in figures, values were estimated manually.
The dataset is associated with a Geoderma manuscript (DOI: 10.1016/j.geoderma.2021.115072) and is one of the results of the Master´s thesis of José Nivaldo Sátiro at the Federal University of Paraná, performed under the supervision of ACM and GB, with the support of various agencies (CNPq, Capes, Newton Fund, Fundação Araucária, NERC and H2020 Marie Curie Actions), and the collaboration of the other authors.