A magnitude 9.0 earthquake and subsequent large tsunami hit the northeastern coast of Japan on March 11, 2011. This resulted in serious damage to the reactors of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP), operated by the Tokyo Electric Power Company. Large amounts of radionuclides were released from the FDNPP, a proportion of which were deposited onto the ground. In this study, we investigated soil radio-cesium contamination of soybean fields in Ibaraki, ~200 km away from the FDNPP. After this accident, we compared the radio-cesium contamination of soybean between the different tillage and cover crop managements.

The experiment variants are: moldboard plow/rotary harrow (MP), rotary cultivator (RC), and no-tilled (NT), three cover type in winter (FL: fallow, RY: rye, and HV hairy vetch) and two nitrogen fertilization rate (0 and 20 kg N ha-1 for soybean production). MP and RC reduced the radio cesium contamination (C_S¹³⁴+C_S¹³⁷) in upper soil layer, although NT leaves large amount of radio cesium on the soil surface. Radio cesium contamination in soybean grains was significantly decreased in MP and RC than in NT in both of 2011 and 2012. We concluded NT system has many benefit for environment conservation, however, inversion of tillage is significant to decrease radio cesium contamination to the crops in several years after nuclear power plant accident.