Increases in pH, Ca2+, and Mg2+ alter the retention of diuron in different soils

Increasing the pH of soils by applying limestone alters the sorption of herbicides and their efficiency at controlling weeds. The objectives of this study were to investigate the effects of increasing the pH and adding Ca2+ and Mg2+ on the sorption and desorption of diuron in different soils, and to evaluate the behavior of the herbicide in cationic solutions to determine whether precipitation is involved in the retention process. Sorption and desorption coefficients (Kf(s) and Kf(d)) were determined based on the Freundlich isotherms using seven soils, which were incubated or not incubated with agricultural limestone. Liming increased the values of Kf(s) and Kf(d) for diuron, even though the organic matter contents of all the soils decreased. The presence of Ca2+ and Mg2+ reduced the concentration of diuron in the aqueous solution. Increasing the pH and Ca2+ and Mg2+ concentrations by applying agricultural limestone increased the sorption and reduced the desorption of diuron in the soils investigated in this study. The behavior of diuron in calcium and magnesium solutions indicates that a precipitation process may be responsible for the increased sorption and reduced desorption of diuron in soils.