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 t ypes. 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. T he 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 ra tio (K-D) varied from 123 to 167 000 mL g(-1) between soils. The log T F 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 solu tion. At K concentrations up to 1 mM, the CF decreased more than 2 ord ers of magnitude with increasing K concentrations. above 1 mM K, the C F was almost unaffected by K supply. A two-parameter nonlinear model f or the log TF was fitted to the K concentrations and K-D values and ex plained 94% of the variance. It is concluded that plant availability o f Cs-137 in mineral soils varies extensively between soils due to diff erences in Cs-137 retention, affecting Cs-137 supply to roots, and to differences in K availability, affecting the Cs-137 root uptake proces s.