Continuous nitrogen fertilization retards the vertical migration of Fukushima nuclear accident-derived cesium-137 in apple orchard soil

• Published in: The Science of the total environment 2020-08, Vol.731, p.138903-138903, Article 138903
• Main Authors: Matsuoka, Kaori, Moritsuka, Naoki, Nukada, Mitsuhiko, Sato, Mamoru
• Format: Article
• Language: English
• Subjects: 133CsBr tracer; A long-term N fertilization experimental orchard; Exchangeable Cs; Soil physicochemical properties; ‘Jonathan’ apple tree
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2020.138903

We monitored the levels of cesium-137 (137Cs) in the soils of five orchards for six years following the Fukushima Daiichi Nuclear Power Plant accident on 11 March 2011 and found that the vertical distribution of accident-derived 137Cs varied significantly among the orchards with varying land-use and fertilizer management. Based on these results, this study evaluated how nitrogen (N) fertilizer management may have affected the vertical migration of 137Cs in the orchard soils. We selected an experimental orchard producing ‘Jonathan’ apples, where a long-term N-fertilizer trial has continued since 1973, with an N-fertilized plot (N plot; N added at 20 g m−2 y−1) and a non-fertilized plot (0 N plot). Five years after the accident, the vertical migration of accident-derived 137Cs was significantly lower in the N plot (2.3 cm) than in the 0 N plot (4.3 cm), suggesting greater 137Cs retention in the surface of the N plot. Application of a cesium bromide (133CsBr) tracer suggested that the retarded vertical migration of 137Cs in the N plot may be related to significantly lower amounts of exchangeable 133Cs and significantly higher proportions of non-exchangeable 133Cs in the upper 2 cm. We did not find any evidence of the aboveground plants contributing to more 133Cs retention in the N plot. However, greater 137Cs retention in the surface (0–2 cm) of the N plot may be due to more dissolved organic carbon (DOC), and high DOC may have contributed to deeper 137Cs migration in both the plots. Our results suggest that continuous N fertilizer application significantly retarded the migration of 137Cs by approximately one-half and resulted in less 137Cs reaching the mobile exchangeable form in the deeper root-zone layers. [Display omitted] •Orchard topsoil retained 42–83% of 137Cs from the Fukushima accident after 5 years.•Long-term N fertilization reduced the soil 137Cs migration rate by about one-half.•N fertilization resulted in less Cs with mobile exchangeable form at the surface.•Reduced 137Cs migration may be due to higher fixation at the surface.•N fertilization may reduce radiation risk via tree roots by slowing 137Cs migration.