Temporal dynamics of ~(137)Cs distribution in soil and soil-to-crop transfer factor under different tillage systems after the Fukushima Daiichi Nuclear Power Plant accident in Japan

摘要

The accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) in Japan in 2011 released a large amount of radionuclides, primarily radiocesium-137 (Cs-137; half-life: 30 years), resulting in long-term contamination of soil and consequently crops. Tillage is a common agricultural management practice that alters the vertical distribution of nutrients in the soil. However, the effect of tillage on Cs-137 contamination in soil and crops over time remains unclear. In this study, we investigated the temporal changes in the vertical distribution of Cs-137 in the soil, concentration of Cs-137 in soybean and cover crops, and the transfer factor (TF) of Cs-137 from the soil to crops under three tillage systems (rotary cultivation [RC], moldboard plow [MP], and no tillage [NT]; main factors) using three cover crops (hairy vetch, winter rye, and fallow weeds; side factors). The amount of Cs-137 in the soil decreased exponentially with soil depth under the NT and RC treatments. By contrast, Cs-137 showed uniform distribution at each soil depth tested under the MP treatment since 2012. The exchangeable Cs-137 demonstrated a similar tendency as Cs-137. The Cs-137 concentration in soybean (including grain and residue) and cover crops decreased exponentially with time. Consistently higher Cs-137 concentration was observed in soybean grains under the NT treatment, suggesting that tillage continuously reduced the concentration of Cs-137 in soybean over 7 years since the FDNPP accident. The TF of Cs-137 from soil to soybean and cover crops decreased continuously over time; however, Cs-137 concentration of soybean grain showed a positive linear correlation with its annual variation rate. Additionally, TF showed a positive logarithmic correlation with Cs-137 relaxation depth in the soil. These results enhance our understanding of the long-term behavior and radioecology of Cs-137 in agroecosystems in Japan since the radionuclide accident. (C) 2019 Elsevier B.V. All rights reserved.