Predicting Molybdenum Adsorption by Soils Using Soil Chemical Parameters in the Constant Capacitance Model

The constant capacitance model, a chemical surface complexation model, was applied to Mo adsorption on 36 samples from 27 soil series selected for variation in soil properties. A general regression model was developed for predicting soil Mo surface complexation constants from four independently measured soil chemical characteristics: cation exchange capacity, organic carbon content, inorganic carbon content, and iron oxide content. The constant capacitance model was well able to predict Mo adsorption on all 36 soil samples. Incorporation of these regression prediction equations into chemical speciation–transport models will allow simulation of soil solution Mo concentrations under diverse environmental and agricultural management conditions without requiring soil specific adsorption data and subsequent parameter optimization.