Effect of topsoil removal and selective countermeasures on radiocesium accumulation in rice plants in Fukushima paddy field

- Effect of topsoil removal practice and fertilizer application on radiocesium uptake by rice plants was investigated.
- Topsoil removal practice for inhibiting the accumulation of radiocesium in rice plants was effective.
- Potassium and nitrogen fertilizers have an opposite effect on the accumulation of radiocesium for rice plants.
- Available countermeasures applied in the paddy fields after the Fukushima nuclear accident are summarized and discussed.

A wide area of paddy fields was contaminated by radiocesium derived from the Fukushima nuclear accident. Implement of agricultural countermeasures is one of the principle methods to reduce the contamination of rice plants. In this study, the effect of topsoil removal measure and fertilizer application on radiocesium uptake by rice plants was investigated over a four-year period. Some other available countermeasures carried out after the Fukushima nuclear accident were also summarized. The results indicate that the effect of topsoil removal measure on the accumulation of radiocesium in rice plants was effective, but the concentration ratio of radiocesium activity concentration between rice plant and soil increased. This may be correlated with the radiocesium imported from irrigation water and relatively high exchangeable radiocesium proportion of plowing soil in the topsoil removal paddy. We summarized four year's data to further confirm that potassium and nitrogen fertilizers had an opposite effect on the accumulation of radiocesium in rice plants. Increasing potassium and reducing nitrogen fertilizer conditions tended to inhibit the radiocesium uptake by rice plants. Moreover, of all the available countermeasures applied in the paddy fields, the most effective countermeasure was the application of phlogopite. However, further analyses are required to confirm the effectiveness of application of phlogopite considering the limited available information.

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