Effect of Phlogopite and Zeolite as a Countermeasure for Radiocesium Uptake Into Herbage

ABSTRACT The effects of applying Finnish phlogopite and artificial zeolite to reduce radiocesium transfer to herbage in a grassland were assessed over a seven‐year period. In all experimental plots, potassium chloride was applied to increase the exchangeable potassium content (ExK) to 400 mg K 2 O/kg in 2015. After 2016, the same amounts of nitrogen, phosphate, and potassium fertilizers were applied twice a year. The grassland renovation and zeolite application (Ze) plots tended to maintain higher ExK levels than the other 3 treatments (no grassland renovation and no materials applied (NMGR), grassland renovation without material application (NM), and grassland renovation and phlogopite application (Phl)) plots up to the fifth year. In the Phl plots, the ExK remained similar to that in the NMGR plots and the NM plots. Generalized linear mixed model (GLMM) analysis by each treatment plot revealed no significant effect of the non‐exchangeable potassium content on transfer factors (TF) in any treatment plot. The TF in the Phl and Ze plots were often significantly lower than those in the NMGR plots. The TF was low when the ExK was high. When the ExK in the Ze plots decreased and reached similar level as that in the other treatments, the TF in the Ze plots was not significantly different from that of the NMGR or NM plots. In the Phl plots, the TF remained lower than that in the NMGR or NM plots, even when the ExK decreased. GLMM analysis estimated that the TF in the Phl plots was 0.39 times that in the NM plots. This effect of phlogopite application is thought to occur due to radiocesium strong absorption by phlogopite, and a single application of phlogopite may reduce the transfer of radiocesium to the herbage over the long term in grassland especially in condition of low soil potassium supply.