RELATIONSHIPS BETWEEN SOIL CHEMICAL-PROPERTIES AND SULFATE SORPTION KINETICS IN PODZOLIC SOILS FROM QUEBEC

The relationships between the slope of three kinetic equations (Elovich, first-order and parabolic diffusion) and commonly measured soil chemical properties were investigated. Twenty-six horizons covering a variety of vegetation types, parent materials and topographic positions were sampled in 18 soil profiles of southern Quebec. A miscible displacement technique in which soils were leached with a 250 mumol SO4 L-1 solution (pH = 4.40) was used to determine time-dependent sulfate sorption. The sum of crystalline plus amorphous inorganic Fe (dithionite-pyrophosphate extraction) was the soil property most closely related to the slope parameters of the Elovich (r = 0.797) and of the parabolic (r = 0.808) equations. Amorphous Al (r = -0.546) and soil pH measured in CaCl2 (r = -0.588) were most strongly correlated to ln -k'a. Organic carbon was not directly related to sulfate sorption as an individual variable but it improved the multiple regression equations used to estimate 1/beta and K0 for the 26 horizons. The Elovich equation was found to give the best representation (average R2 = 0.978) of sulfate sorption kinetics. Good results were also obtained using the first-order equation (average r2 = 0.976) although a marked deviation of experimental data from linearity was observed at high surface coverage. The relatively close relationship between predicted and calculated values confirmed the potential of equations based upon commonly measured soil properties to estimate the slope parameter of kinetic equations describing sulfate sorption by Podzolic soils.