EFFECT OF CHLORIDE AND SULFATE ANIONS ON THE CHEMICAL CHARACTERISTICS OF SOME ACID SOILS

Abstract

Experiments were done to compare the cation exchange and soil solution chemistry characteristics of seven acid soils in the presence of chloride and sulfate ions. The pH of the soil suspensions and degree of base saturation of equilibrated soil samples in CaSO4 solutions were higher than those of CaCl2-equilibrated samples. A comparison of the soil solution chemistry of Al in the presence of Cl and SO4 ions showed significant differences in the distribution of aluminum ion species. Even though the total aluminum (AlT) was greater in CaSO4 suspensions than in corresponding CaCl2 suspensions, trivalent Al (Al3+) was much smaller in CaSO4 suspensions, e.g. 93.4% of aluminum was present as Al3+ in CaCl2 suspensions compared to 36.0% in CaSO4 suspensions. In CaSO4 suspensions, 60.0% of aluminum was present as monovalent AlSO+4, which was probably not as effective as trivalent Al in competing with basic cations in occupying exchange sites. This reveals that in SO4 systems, a substantial amount of Al (60%) was present in a form which could easily move in the soil profile or could leach out of the soil profile and thus to the aquatic environment.