Concentrations of Cs-137 and K in soil solution predict the plant availability of Cs-137 in soils

The plant availability of Cs-137 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 Cs-137 and incubated For 41 days prior to 19 days plant growth. The plant-soil Cs-137 concentration ratio (TF) varied from 0.002 to 2.6 g g(-1) between soils. The soil-soil solution Cs-137 concentration ratio (K-D) varied from 123 to 167 000 mL g(-1) between soils. The log TF was negatively correlated with log K-D, but the correlation was weak (R-2 = 0.10). The plant-soil solution Cs-137 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 K-D values and explained 94% of the variance. It is concluded that plant availability of Cs-137 in mineral soils varies extensively between soils due to differences in Cs-137 retention, affecting Cs-137 supply to roots, and to differences in K availability, affecting the Cs-137 root uptake process.