The Effect of Gypsum Amendments on the Displacement of Exchangeable Aluminum From Acid Bt Horizons.

Two acidic silt loam soils, Beauregard and Gigger were used in a study involving Ca movement and Al displacement from 15.2 cm laboratory soil clumns. Each column was uniformly packed to the appropriate bulk density. The top 5.1 cm portion of each column contained soil pre-mixed with powdered gypsum at rates of 0, 1 and 2 equivalents of the exchangeable Al. Calcium movement and Al displacement in the soil columns were accomplished by applying distilled-deionized water at a constant flow rate and the effluent was analyzed. In addition, a pulse containing dissolved gypsum at the rate of 4 Al equivalents was applied at a constant flow rate to unamended uniformly packed soil columns. Results from leachate analysis indicate that the Beauregard soil retained more Ca than the Gigger soil. Ten PV of leachate were found to be sufficient for the removal of most of the exchangeable Al. However, Al was displaced earlier from the Gigger than the Beauregard. The displacing Ca was uniformly distributed within each soil column at the termination of the miscible displacement experiments. Total amount of Al leached were considerably less than the initial exchangeable Al for both soils. This was also true when the exchangeable Al at the termination of each experiment, was taken into account. Therefore, a portion of the Al was converted to non-extractable form. Results of (\u2745)Ca and (\u2736)Cl displacement provided essential data on Ca and SO(,4) soil columns. Leachates were also analyzed for Mg, Na, Fe and Mn in order to predict trends typical of cations and anions movement in these soils. The pH of the effluents increased from 4.0 to over 6.0 as leaching proceeded. Results from this research suggest that shallow gypsum treatments will be capable of providing Ca and SO(,4) while displacing significant amounts of subsoil Al from permeable acid soils that receive sufficient rainfall