Effects of plowing on vertical distribution of radioactive Cs and soil physicochemical properties in temperate pastures

This study investigated the effects of plowing on the vertical migration of radioactive Cs, air dose rate, and soil physicochemical properties in temperate pastures after radioactive pollution from the 2011 Fukushima Daiichi Nuclear Power Plant accident. The study area consisted of three plowed pastures (decontamination treatment) and one non-plowed pasture at the Kawatabi Field Science Center of Tohoku University, 150 km north of the nuclear power plant. Air dose rate was measured at the top, middle, and bottom of the slope of each pasture. A profile pit (1 m × 3 m) was excavated at each location. Plants, litter and soil samples (from 0 cm to the parent material layer) were collected from all locations during the summer of 2014 to determine the radioactive Cs concentration. Particle size distribution and bulk density of the soil samples were also measured. Air dose rate was higher on the non-plowed (0.090–0.097 μSv h⁻¹) than that on the plowed (0.047–0.073 μSv h⁻¹) pastures. Radioactive Cs concentration was high in the litter layer (207–475 Bq kg⁻¹ dry matter [DM]) and the topsoil (0–2.5 cm depth; 412–1139 Bq kg⁻¹ DM) in the non-plowed pasture. In the plowed pastures, these variables did not differ within the 0–40 cm layer. In the non-plowed pasture, there were high sand (37.0%) and low silt (61.4%) proportions at 10–20 cm and the topsoil had a high bulk density. In the plowed pastures, these variables were similar within the 0–20 cm layer. The bulk density (P < 0.001) and organic matter content (P < 0.05) had significant relationships with the concentration of radioactive Cs. These results indicate that plowing reduced air dose rate.