Concentrations of ¹³⁷Cs and K in Soil Solution Predict the Plant Availability of ¹³⁷Cs in Soils

Abstract

The plant availability of 137Cs in soils varies widely between soil types. The source of this variation was analyzed in a pot trial. Thirty topsoils covering a wide range in textural classes were contaminated with 137Cs and incubated for 41 days prior to 19 days plant growth. The plant−soil 137Cs concentration ratio (TF) varied from 0.002 to 2.6 g g-1 between soils. The soil−soil solution 137Cs concentration ratio (KD) varied from 123 to 167 000 mL g-1 between soils. The log TF was negatively correlated with log KD, but the correlation was weak (R 2 = 0.10). The plant−soil solution 137Cs concentration ratio (CF) was however significantly related to the K concentration in soil solution. At K concentrations up to 1 mM, the CF decreased more than 2 orders of magnitude with increasing K concentrations. Above 1 mM K, the CF was almost unaffected by K supply. A two-parameter nonlinear model for the log TF was fitted to the K concentrations and KD values and explained 94% of the variance. It is concluded that plant availability of 137Cs in mineral soils varies extensively between soils due to differences in 137Cs retention, affecting 137Cs supply to roots, and to differences in K availability, affecting the 137Cs root uptake process.