Transfer factors of radiocesium to brown rice in the decontaminated paddy field

Paddy fields contaminated with radionuclides released from the Tokyo Electric Power Company’s Fukushima Daiichi Nuclear Power Plant were decontaminated between 2012 and 2014 by removal or cleaning of the surface layer of soil. The effects of application of potassium fertilizer and soil amendment (zeolite) on the radiocesium concentration in brown rice, rice growth and grain yield of rice grown in these paddy fields were examined. The concentrations of radiocesium in soil and brown rice were decreased by the decontamination, but the ratio of decrease differed with the fields. Transfer factors (TF) from soil to brown rice (ratio of radiocesium concentration in brown rice to that in the soil) were related to the exchangeable potassium (Ex-K) concentration in the collected soil at harvest, excluding the irregular data. This relationship in decontaminated plots was not distinguishable from that in non-decontaminated plots. This suggested that the field management maintaining a high Ex-K concentration in soil should be applied to inhibit the uptake of radiocesium by rice in decontaminated paddy fields as well as in non-decontaminated paddy fields. The application of zeolite increased the Ex-K concentration in soil and this effect was observed even in the following season. Available nitrogen concentration in soil was decreased by the decontamination and the negative relationship was observed between the available nitrogen concentration and grain yield. This suggested that additional nitrogen fertilizer should be applied to the paddy field when the available nitrogen concentration was decreased by decontamination.