Radiocesium absorption in soybean

Radioactive materials that were released during the nuclear accident contaminated the soil and agricultural products. The monitoring inspections indicated that the ratio of soybean plants that accumulated more than 100 Bq/kg radiocesium, the new standard value for radiocesium, was higher than the values reported for rice and wheat in these three years. The decreasing tendency of this value in soybean was lower compared to that in rice. Though there are some reports about absorption of cesium for crops, it is not clear why the radiocesium concentration of soybeans is still remaining higher than the other crops. Focusing on this point, the process for absorption of radiocesium under different concentration of nitrogen and potassium fertilizer as well as the radiocesium distribution in the soybean was studied. In the field experiment, differences in radiocesium concentration were observed among the tissue in the soybean. The radiocesium concentration in the root was higher than that of the aerial parts. The ratio in potassium to cesium was different between the aboveground and underground part. In the case of nitrogen fertilizer, the concentration of radiocesium in seeds was higher in nitrogen-fertilized plants than that grown without fertilizer. It was found that the special care is required to start farming of the soybean in fallow fields evacuated after the accident or on in the fields where rice was grown before, which tend to contain higher available nitrogen than the regular cultivating fields. (author)