Nature of Soil Acidity in Soils Developed on Granite Gneiss and Mahananda Alluvium

The sedentary soils developed on granite gneiss were more acidic than alluvial soils developed on Mahananda alluvium. while hydrolytic acidity was higher in alluvial soils than in the sedentary soils. The exchange and hydrolytic acidity decreased down the depth of the pedons. The hydrolytic acidity was higher than the exchange acidity. These forms of acidity were mainly contributed by Al³⁺ ions. The extractable Al³⁺ by unbuffered KCl solution was lower than those extracted by buffered NaOAc (pH 7.8) and NH₄OAc(pH 7.0) due mainly to the fact that was pH-dependent. The prediction equation showed that 53.6 per cent of variation in pHw was governed by organic carbon, exchange acidity, hydrolytic acidity, exchangeable and NaOAc and NH₄OAc extractable Al.