In 2011, Great East Japan Earthquake and subsequent tsunami caused severe damage on the TEPCO’s nuclear power plants in Fukushima prefecture. A large area of agricultural fields in Eastern Japan was suffered by substantial amount of radioactive materials (especially radiocesium) and tremendous efforts has been taken to remediate the contaminated fields. Though phytoremediation was expected to be effective to remove radiocesium, it did not work at least in this area. Actually physical decontamination was carried out, while it is still required to mitigate the transfer of the remaining radiocesium to the crops. For this purpose potassium application is adopted as a reliable method.