Factors responsible for radiocesium transfer from soil to rice and soybeans after the Fukushima Daiichi Nuclear Power Plant accident

This is the authors' abstract. We don't add key points for this paper.

Understanding the effects of multiple factors on the accumulation of 137 Cs in grain is critical for determining the intensity and duration of countermeasures to reduce 137 Cs contamination of agricultural products. Here, using survey data of 137 Cs concentration in rice and soybean collected from the fields of farmers in Fukushima Prefecture, Japan, from 2012 to 2020, we developed comprehensive statistical models to evaluate grain- 137 Cs simultaneously and quantitatively with several factors. The statistical models indicated that the exchangeable 137 Cs concentration in soil (Ex- 137 Cs) was a more suitable indicator of soil 137 Cs contamination than the total 137 Cs concentration in the soil for predicting grain- 137 Cs. Soybeans exhibited 12-fold higher grain- 137 Cs than rice under the same Ex- 137 Cs and exchangeable potassium concentration in the soil (Ex-K), primarily because of the higher 137 Cs uptake per dry matter production. The degree of reduction in grain- 137 Cs estimated by Ex- 137 Cs with increasing Ex-K was similar in rice and soybeans, suggesting that the inhibitory mechanism of K supply to the root zone on 137 Cs uptake was similar in both crops. However, the ratio of Ex- 137 Cs to total 137 Cs in soil was more sensitive to Ex-K in soybean than in rice, indicating a difference in the dynamics of Ex-K and Ex- 137 Cs between rice paddy fields and soybean upland fields. These results show that the dynamics of Ex- 137 Cs in soil and the response to Ex- 137 Cs are key factors regulating the difference in grain- 137 Cs activity concentration between soybean and rice. • Models constructed by using 9-year survey data predict grain 137 Cs concentration. • Exchangeable 137 Cs in soil was a more suitable indicator than the total 137 Cs in soil. • Soybeans had a 12-fold higher grain 137 Cs concentration than rice in same soil. • Response to exchangeable 137 Cs regulated differences in grain 137 Cs between crops.