Radiocesium distribution caused by tillage inversion affects the soil-to-crop transfer factor and translocation in agroecosystems

Abstract

This study reports the translocation of cesium-137 (137Cs) into deep soil layers, and the 137Cs transfer from soil to soybean in farmland under three tillage (no tillage, NT; rotary cultivation, RC; moldboard plow; MP) treatments and an undisturbed grassland (GL) at eight years after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident on 11 March 2011 in Japan. Tillage influences the 137Cs distribution in the 0–30 cm of soil; the distribution of 137Cs in the soil was uniform under RC and MP treatments, while in the grassland, most 137Cs was concentrated on the soil surface (0–2.5 cm). The center of vertical 137Cs radioactivity concentration (the thickness of the soil from surface which containing half of the 137Cs inventory) in GL was 5.5 cm, which was shallower than that in farmland (9.5 cm in NT, 13.6 cm in RC and 15.2 cm in MP). Hence, the total translocation distance of 137Cs 8 years after FDNPP accident showed the following trend: GL (2.4 cm) < NT (7.0 cm) < RC (10.0 cm) < MP (12.3 cm). Meanwhile, a significant positive correlation was observed between 137Cs radioactivity concentration and organic carbon and nitrogen content in the soil. However, the 137Cs radioactivity concentration in soybean grains was negatively correlated with the center of vertical 137Cs radioactivity concentration but positively correlated with the ratio of exchangeable 137Cs (ExCs) and K content in the soil. The ExCs/K and 137Cs distributions in the soil were combined into a statistical model to predict the 137Cs radioactivity concentration in soybean grain. The results revealed the magnitude of the impact of 137Cs distribution on the 137Cs transfer from soil to crop. The addition of the 137Cs distribution dramatically improved the accuracy of the prediction model of 137Cs radioactivity concentration in soybean.