Potassium buffering characteristics and detection of soils with challenges in evaluating radiocesium uptake risk of crops by exchangeable potassium

ABSTRACT In surrounding areas influenced by the Fukushima Dai-ichi Nuclear Power Plant accident, the radiocesium uptake by crops was evaluated based on soil exchangeable K. As risk evaluation does not function effectively in several fields, K buffering was characterized using quantity/intensity (Q/I) relationship analysis to evaluate the availability of exchangeable K. The results of the analysis clearly explain the difficulty in the risk evaluation: i) difficulty in increasing exchangeable K, owing to retention as non-exchangeable K by vermiculite; ii) difficulty in retaining exchangeable K due to low K buffering capacity, reflecting the lack of K-selective clay minerals; and iii) difficulty in increasing soil solution K intensity due to high K buffering capacity, reflecting the abundance of K-selective clay minerals. Among the parameters calculated from the Q/I relationship analysis, β values, corresponding to the retention rate of loaded K to the soil, for total K (βt), exchangeable K (βe), and non-exchangeable K (βn) would be useful as simple indicators of soils with a predicament in the risk evaluation of radiocesium uptake by crops through exchangeable K. These soils showed distinctively low βt values (0.18 or lower), high βe value (0.37 or higher), or high βn/βt ratio (0.53 or higher).