Sulfate solutions were mixed with a soil that had a high capacity to adsorb sulfate, and 3 techniques were used to see whether the strength of the link between sulfate and the soil particles increased with time. The techniques were measurements of the change in sulfate concentration in the soil solution; of the change in availability to plants; and of desorption of sulfate. All 3 techniques showed that there were, indeed, slow changes. These were similar to, but much slower than, those observed for phosphate, molybdate and fluoride. This suggests that such behavior is a characteristic of specifically adsorbed anions, not just of phosphate.