ABSTRACT
Addition of phosphate to soils is a common agricultural practice. As phosphate anions are known to adsorb strongly on many soil minerals, the presence of important amounts of phosphorus fertilizers is likely to cause a noticeable decrease in the adsorbing properties of soils with respect to other anions, e.g., anionic pesticides. This chapter studies the competitive adsorption of the anionic herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) and phosphate on various soils in southwestern Spain. Many adsorbing properties of soils can be related with variable charge surfaces present in the clay fraction. A spectacular increase in 2,4-D adsorption was observed in both soils. Data obtained with kaolinite suggest that no differences exist for this mineral when different alkaline cations are used in the electrolyte.
