Prediction of persistence of fertilizer-derived cadmium in Oregon agricultural soils using equilibrium modeling and fertilizer release kinetics

Organic farming has become a multimillion dollar industry and while much emphasis is put on subsequent fertilizer inputs onto these fields, very little consideration is given to the prior fertilization activities of these soils. For a farm to be certified organic it means no harmful chemicals have been applied for at least three years.;The Kd values and adsorption trend of the soil sites was Pendleton > Klamath > Hyslop > Hermiston. The cadmium Kd values were most correlated to the pH of the soils (R2=0.94). The buffer capacity of the soils was highly correlated to the clay content (R2 = 0.98). The adsorption coefficients were important for predicting the doubling times of cadmium in the soils (Hermiston, 4.8yrs > Hyslop, 3.7yrs > Klamath, 2.9 yrs> Pendleton 2.3 yrs). Precipitation was not the most important parameter in predicting the mass loss due to leaching after three years (46.2, 19.9, 16.7 and 8.3 mg/ha-yr for Hyslop, Hermiston, Pendleton and Klamath respectively). The period was found to have a negligible effect on the background concentrations of cadmium in agricultural soils.;Scanning electron microscopy, X-ray diffraction and column displacement experiments were used to investigate the fertilizer kinetics of fertilizer-derived cadmium and the processes controlling the release of fertilizer-derived cadmium were found to be a Cd-phosphate phase, possibly cadmium hydroxyapaptite, and iron oxides. The release of Cd from phosphate fertilizer was slow so a local equilibrium model was appropriate for agricultural soils.;The overall hypothesis tested by this research was that equilibrium adsorption models can adequately represent the behavior of fertilizer-derived cadmium in Oregon agricultural soils and that such model results can be easily incorporated into risk assessment models, transport study models and persistence studies for organic or other sustainable farming considerations. Soil chemistry and soil characterization were used to calculate the doubling time and mass flux of cadmium-derived fertilizer in loamy and sandy agricultural soils with a rich farming history. We also investigated the processes controlling the release of fertilizer-derived cadmium in the micro scale zone around the fertilizer to determine if a local equilibrium model was appropriate for explaining cadmium behavior in agricultural soils.