Abstract
To assess the risk of transfer of radiocesium from soil to brown rice on the soil with low exchangeable potassium (ExK2O) content, seedlings of rice cultivar "Tennotsubu" were transplanted to 500 cm2 Wagner pots filled with paddy soil collected from 21 sites in Fukushima prefecture, and grown to maturity without potassium fertilizer in 2015. ExK2O content of soil before and after cultivation, and radiocesium (137Cs) concentration of rough brown rice, straw and pot soil were measured to examine the effects of ExK2O content of soil on the transfer of radiocesium from soil to rough brown rice. ExK2O content of soil varied significantly with the site, and the contents at 12 sites were lower than 5 mg 100 g–1. The concentration of 137Cs in rough brown rice varied significantly with the site, in the range of 2.8 to 68.3 Bq kg–1. Transfer factors of 137Cs from soil to rough brown rice (ratio of 137Cs concentration in rough brown rice to that in the soil), obtained from this pot experiment, was markedly higher than those obtained in the field cultivation, because of the lower ExK2O content of soil in the pot. Moreover, the lower the ExK2O content of soil, the higher the ratio of 137Cs concentration in rough brown rice to that in straw, suggesting that 137Cs translocation to brown rice is enhanced by the decrease of potassium concentration in the rice shoot.
