EXCHANGE AND SOLUTION-PHASE CHEMISTRY OF ACID, HIGHLY WEATHERED SOILS .1. CHARACTERISTICS OF SOILS AND THE EFFECTS OF LIME AND GYPSUM AMENDMENTS

Exchange and solution phase characteristics were evaluated on surface and subsoil horizons of 60 acid, highly weathered soils in the unamended state, and on 39 of the surface horizons following addition of CaCO3 or CaSO4.2H2O. Soil solutions from unamended surface samples were dominated by Na (median concentration 0.65 mM), while the other major cations were present at lower levels (median concentrations: Ca, 0.09; Mg, 0.14; K, 0.28 mM). This pattern was more pronounced in the subsoil samples where the median concentrations of the nutrient cations were less-than-or-equal-to 0.05 mM, whereas the median concentration of Na was 0.28 mM. The cation exchange capacity of surface samples was dominated by Ca, Mg and Al, while Al was the major exchangeable cation in the subsoil. Addition Of CaSO4.2H2O decreased soil solution pH and increased electrical conductivity and the concentration of Ca, Mg, Na, K and Al in the soil solution. The soil solution pH change resulting from CaSO4.2H2O addition could not be predicted on the basis of the characteristics of the soil in the unamended state.