The Effect of Continuous Application of Organic Materials and Flooded Sand Inflow on the Cs Concentration in Rice after Stripping the Cs Contaminated-Top Soil Off at Iitate Village in Fukushima Prefecture.

Plow layer which is important for agriculture was polluted with Cs-134 and Cs-137 by the accident of the Nuclear Power Plant in 2011. The farmers in Iitate Village have been forced to evacuate from their village. They are at the crossroads whether or not they will come back to the village by some time in 2017 after the decontamination work. Wiping off harmful rumors or misinformation about Cs contamination of foods are very important for farmers who want to go back and make living by agriculture. We have been investigating radiocesium transfer to rice plants from soil at paddies with continuous application of organic materials after stripping the contaminated top soil off since 2013. Field plots were prepared for three treatments with and without different organic resources: 1) addition of rice straw harvested from the plots in the previous year; 2) addition of manure compost; and 3) no addition after decontamination in 2013. Part of the plots received flood sand containing the radiocesiums in September 2015. In 2015 the Cs concentrations of stems and leaves buried with the flooded sand, containing 11.93±3.32, 9.70±2.9, 8.86±2.17 Bq/kg Cs-134, and 49.42±3.32, 32.32±2.95, 35.86±2.17 Bq/kg Cs-137, respectively, exceeded ones observed in 2014. However, the Cs concentrations of brown rice were < a detecting limit. The Cs contamination of the stems and leaves was resulted from clay particles, adsorbing Cs, remained on the surfaces of the stems and leaves. The result showed that the transfer of Cs from the soil to rice was little evident although the flooded sand recontaminated the site with Cs. We are continuing the rice-growing experiment this year at the site with similar treatments but splitting the original treatments into two, with flooded sand and without flooded sand. Seedlings of Koshihikari,a japonica variety, were transplanted on May 29, 2016. We will discuss the results of the Cs concentration in various parts of a rice plant.