Influence of the nonexchangeable potassium of mica on radiocesium uptake by paddy rice

A pot cultivation experiment was conducted to elucidate the influence of the nonexchangeable potassium (K) of mica on radiocesium (Cs-137) uptake by paddy rice (Oryza sativa L. cv. Koshihikari), and to evaluate the potential of mica application as a countermeasure to reduce radiocesium transfer from soil to paddy rice. The increase in the exchangeable K concentrations of soils, measured before planting, due to mica (muscovite, biotite, and phlogopite) application was negligible. However, in trioctahedral mica (biotite and phlogopite)-treated soil, the release of nonexchangeable K from the mica interlayer maintained the soil-solution K at a higher level during the growing season in comparison to the control, and consequently decreased the Cs-137 transfer factor for brown rice (TF). The sodium tetraphenylboron (TPB)-extractable K concentration of the :soils, measured before planting, was strongly negatively correlated with the TF, whereas the exchangeable K concentration of the soils, also measured before planting, was not correlated with the TF. Therefore, we conclude that TPB-extractable K is more reliable than exchangeable K as a basis of fertilizer recommendations for radiocesium-contaminated paddy fields. Phlogopite-treated soils exhibited higher TPB-extractable K concentrations and lower IT values than biotite-treated soils. We thus conclude that phlogopite application is an effective countermeasure to reduce radiocesium uptake in paddy rice. (C) 2015 Elsevier Ltd. All rights reserved.