Predicting radium availability and uptake from soil properties

Results of a potted soil experiment to determine the soil and plant factors ruling radium availability and uptake by ryegrass and clover are described. Nine soils with distinct soil characteristics were spiked with 226Ra. They were thoroughly characterized. The solid liquid partitioning coefficient, Kd , ranged from 38 L kg-1 to 446 L kg-1 and was linearly related to cation exchange capacity (CEC) and organic matter (OM) content. The soil-to-plant transfer factor (TF) was significantly affected by the chemical properties of the soils and ranged from 0.054 kg kg-1 to 0.719 kg kg-1 for ryegrass and from 0.034 kg kg-1 to 1.494 kg kg-1 for clover. Overall, no significant difference in TF between ryegrass and clover was observed. TF was related to Kd, to CEC, OM and the calcium concentration in the soil solution Radium flows were calculated from the radium concentration in soil solution and evapotranspiration, to predict total radium uptake derived from shoot radium concentration and biomass yield. It was found that radium uptake could be predicted from the radium flow. Higher predictability was obtained when relating total radium uptake to a radium flow considering competition effects at the root surface by the bivalent cations.