Verification of Effects on Crops and Surrounding Environment in Agriculture Using Radioactively Contaminated Grass Silage Compost Made by Aerobic Ultrahigh Temperature Fermentation

Abstract The Fukushima Daiichi Nuclear Power Plant (Tokyo Electric Power Co. Ltd.) accident caused by the Great East Japan Earthquake (11 March 2011) contaminated farmland, grassland, and grass silage in the Tohoku region of Japan with radioactive cesium. In previous studies, we have converted contaminated pasture grasses to compost by employing aerobic ultrahigh temperature fermentation and this showed below acceptable levels of radioactivity. In the present study, we verified whether the decontaminated compost could be safely applied to grassland. A 1200 m 2 pastureland (average 320 Bq/kg) in Kurihara-city, Miyagi-prefecture, Japan, was divided into 6 plots, of which 4 plots were treated with 2, 5, 10, and 30 kg of grass silage compost (297 Bq/kg) per m 2 . In the control plot, chemical fertilizers or nonradioactive cattle manure were applied. After those plots were plowed, orchard grass ( Dactylis glomerata ) was sown and grown for about 2 months. No significant changes in soil radiocesium concentrations or air dose rates were observed in the pastures during and after the cultivation period. The water quality of the river in the vicinity of the pasture was also not affected. The radiocesium levels in the grass harvested from all plots, including the test plot with 30 kg per m 2 of application, were below the detection limit (below 20 Bq/kg), less than one-fifth of the provisional value (100 Bq/kg) for forage. These results demonstrate that radioactive contaminated grass silage compost can be safely applied to actual pastures.