SULFATE SORPTION IN SOILS UNDER ACID DEPOSITION - MODELING FIELD DATAFROM FOREST LIMING

Sulfate sorption can modify the reaction of a soil to acid depositions . Different models of this process exist. In a preceeding paper the ad sorption isotherm and the solubility product modeling approach have be en compared and a solubility product model has been introduced. The la tter model is tested using a forest liming experiment. Concentration d ata from canopy drip and seepage covering a 20-yr observation period a re used as 3-yr moving averages. The model assumes a steady seepage fl ow and uses only one 1-m compartment. The model considers joint chemic al equilibria for gibbsite, jurbanite, cation exchange, and complexati on. The seepage pH and concentrations of Al and sulfate under the unli med reference plot can be modeled if a reduced CEC and a free paramete r function for alkalinity production are used. The sulfate desorption caused by liming can be explained by the model. It is concluded that s orbed sulfate contributes to the lime requirement of an acidified soil .