The Effect of Continuous Application of Organic Materials on the Soil Fertility after Stripping the Cs Contaminated-Top Soil Off at Iitate Village in Fukushima Prefecture.

An agricultural beneficial top soil was contaminated by radionuclides, e.g., 134-Cs and 137-Cs, just after the accident of the Nuclear Power Plant in 2011. Farmers in Iitate Village have been forced to evacuate from their home ever since after the accident. Decontamination work is needed for villagers to return to village. However, decontamination by stripping the top soil off may attribute to decreases in soil fertility. We had expected the natural breakdown of organic matter to quickly recover the fertile top soil in agricultural fields. We tried field experiment transplanted rice crop in the three treatments of paddy fields, such as 1) with rice straw harvested last year in Iitate Village to build a recycling farming system that was successfully established by villagers before the accident, 2) with manure compost and 3) with nothing after decontamination in 2013. Transfer rate of the radionuclides from the rice straw harvested last year to new rice crop had almost not detected. Rice crop yields are the best in the 1) field with rice straw and the worst in the 3) field with nothing. Although it is normally said that the gas generated during the season of the breakdown of rice straw might damage rice growth when we apply rice straw in spring, no damage was observed in our site where we mixed organic matter into the soil in spring in 2013. However, the expectation that rapid degradation of rice straw in summer might cause the high concentration in new rice crops was reported, we must check the last results were not temporariness to revive agriculture in Fukushima. We started a field experiment checking the effect of continuous application of organic matter on the radionuclides concentration in new rice crop and the yields this year. We will show the results of this year trial.