Uranium accumulation in agricultural soilsas derived from long-term phosphorus fertilizer applications

• Main Author: Sun, Yajie
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag 2020
• Subjects: Kola Peninsula; in Rengen; Iceland; kola peninsula
• Online Access: https://juser.fz-juelich.de/record/890450; https://juser.fz-juelich.de/search?p=id:%22FZJ-2021-00966%22

It is well known that uranium (U) in mineral phosphorus (P) fertilizers may accumulate in agricultural soils; yet, this U accumulation occurs at different rates, likely depending on the type of fertilizer used. To substantiate this assumption, the aims of my thesis were: i) to quantify the accumulation rates of fertilizer-derived U in different long-term agricultural field experiments with P fertilized soils of central Europe, and ii) to contrast this with data from longterm experimental sites on volcanic soils that require higher amounts of P fertilizers for optimal crop production, and iii) finally to explain the variations of U accumulation rates by an assessment of the formation mechanisms and stocks of U in major phosphate rocks (PRs) deposits of the world. Soil samples were taken from the surface soils and selected depth profiles of seven long-term experiment sites, i.e. at the grassland fertilization trials in Rengen (Germany), Park Grass (Rothamsted, UK), as well as in Geitasandur and Sámstaðir (Iceland), and the agricultural field experimental sites in Thyrow (Germany), Askov (Denmark), Broadbalk (Rothamsted, UK), Uranium concentrations were analyzed after microwave-assisted acid digestion by nitric acidor/and a complete digestion by lithium meta/tetraborate. In addition, I assessed U concentrations and the natural stable oxygen isotope compositions of phosphate (δ$^{18}$OP) in PRs as potential indicators for the genesis of the U in PRs from different deposits all over the world. My results revealed a wide range of U accumulation rates in soils, ranging from 0-310 μg U kg$^{-1}$ yr$^{-1}$ in the monitored fields. Uranium accumulation was small when the P fertilizers were derived from igneous PRs from Finland and Kola Peninsula, as used for sites in Askov (< 0.4 μg U kg$^{-1}$ yr$^{-1}$; <1.2 g ha$^{-1}$ yr$^{-1}$ (20 cm)) and Thyrow (0.6 μg U kg$^{-1}$ yr$^{-1}$; 2.3 g ha$^{-1}$ yr$^{-1}$ (24 cm)), respectively, or when basic slag was applied as used for the Rengen (1.2 μg U kg$^{-1}$ yr$^{-1}$; ...