Development and validation of a terrestrial biotic ligand model predicting the effect of cobalt on root growth of barley (Hordeum vulgare)

A Biotic Ligand Model was developed predicting the effect of cobalt on root growth of barley (Hordeum vulgare) in nutrient solutions. The extent to which Ca²⁺, Mg²⁺, Na⁺, K⁺ ions and pH independently affect cobalt toxicity to barley was studied. With increasing activities of Mg²⁺, and to a lesser extent also K⁺, the 4-d EC50_Co²⁺ increased linearly, while Ca²⁺, Na⁺ and H⁺ activities did not affect Co²⁺ toxicity. Stability constants for the binding of Co²⁺, Mg²⁺ and K⁺ to the biotic ligand were obtained: log K_CoBL = 5.14, log K_MgBL = 3.86 and log K_KBL = 2.50. Limited validation of the model with one standard artificial soil and one standard field soil showed that the 4-d EC50_Co²⁺ could only be predicted within a factor of four from the observed values, indicating further refinement of the BLM is needed.