Consecutive Field Trials of Rice Cultivation in Partially Decontaminated Paddy Fields to Reduce Radiocesium Absorption in the Iitate Village in Fukushima Prefecture

Abstract

We performed consecutive field trials of rice cultivation to reduce radiocesium (134Cs and 137Cs) absorption by rice in a partially decontaminated paddy soil in the Iitate Village in Fukushima prefecture, Japan. People had evacuated this area because of the high levels of radioactive contamination caused by the nuclear disaster in 2011 at the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power. The radiocesium concentrations were measured for paddy soil and for lowland rice grown on variously decontaminated paddy soil in 2012 and 2013. The results show that the radiocesium concentration in the brown rice cultured in the fields of Sasu and Maeda with 2000–6000 Bq/kg dry weight (0–15 cm average soil depth) was below 40 Bq/kg, which is below the Japanese new standard for food (100 Bq/kg). In addition, the radiocesium concentration in the brown rice depended on the decontamination level of the paddy soil. In addition, the radiocesium concentration in the rice was reduced depending on the exchangeable K content of the soil, which plateaued around 20 mg K2O per 100 g dry soil. However, in 2013, in a test field of Komiya where the radiocesium concentrations were higher than 8000 Bq/kg dry weight, brown rice with more than 100 Bq/kg was harvested, indicating the need for further decontamination. Overall, our results show that decontamination and additional K fertilization can reduce the radiocesium concentration in rice to less than the new standard, and that we could resume rice cultivation in the Iitate village by rather practical way.