Adsorption and Desorption of Boron in Column Studies as Related to pH: Results and Model Predictions

Abstract

Reuse of agricultural drainage waters, treated municipal wastewaters, and brackish groundwaters is often impaired by elevated concentrations of B. Boron is an element with a narrow concentration range between deficiency and toxicity for plants. Knowledge of the B concentrations in soil solution and transport of B out of the root zone is essential for management of wastewaters. Prediction of B concentrations in the root zone requires consideration of soil adsorption and desorption of B, which are dependent on soil properties and solution composition, especially pH. We examine B transport in soil by first applying a 0.08‐mmol L−1 B solution to three arid‐land soils from southern California and subsequently leaching the soils with a low B solution. The experiment was conducted with irrigation water at pH 6.0 and 9.0. The data showed that transport was highly pH dependent. Results from the column experiments were generally well predicted using the UNSATCHEM transport model with the B subroutine that includes the constant capacitance model and prediction of the model constants for each soil based on the specific soil properties. Use of a single set of average constants for all soils in combination with a calculated surface area provided a less satisfactory fit to the experimental data, especially at elevated pH. These results indicate that B transport can be predicted without the need for time‐consuming and soil‐specific determinations of B adsorption characteristics if we utilize predictive relations to predict the CCM constants from individual soil properties.