This paper discusses the radioactive contamination of soybean fields in Ibaraki from 2011 to 2013 after the 2011 accident at the Fukushima Daiichi nuclear power plant (FDNPP). After the accident, large quantities of radioactive material were released, some of which was deposited on the ground. However, although agricultural produce from this region has levels of radiocesium below the maximum permitted concentration in food, people refrain from buying agricultural produce from this region, and negative information still persisted in 2015. In this study, as part of efforts to further reduce levels of radiocesium and restore consumer confidence in agricultural products from Ibaraki prefecture, we examined the effects of different tillage systems (moldboard plow, rotary cultivation, and no tillage) and three types of winter cover crop (fallow weeds, rye, and hairy vetch). Measurements taken before tillage in 2011 showed that the radiocesium concentration in the surface soil (0-2.5 cm) was higher than that in deeper layers (2.5-15 cm). However, after rotary cultivation in 2012, the concentration in the 0-2.5 cm layer was reduced and that in the 2.5-15 cm layer was increased. The concentration in weeds was significantly higher than those in the hairy vetch or rye during 2011 to 2013. The transfer factor (TF) in weeds was higher than that in hairy vetch or rye from 2011 to 2013. The radiocesium concentration and TF in soybean crop residue were higher than harvested soybeans those in from 2011 to 2013, although those in the soybeans were lower than the limits in food determined by the Ministry of Health, Labor and Welfare of Japan. The radiocesium contamination of soil, soybeans, and cover crops has decreased every year since the FDNPP accident. To further reduce the uptake of radiocesium into crops and restore market confidence in agricultural produce from Ibaraki, it is necessary to conduct more studies on the relationship between radiocesium and soil and crops.
2017 by Agricultural and Forestry Research Center, University of Tsukuba