Laterite soils of Orissa belonging to Alfisols. Ultisols and inceptisols have pH dependent acidity varying from 3.1 to 11.8 cmol (p+)kg−1 and are mainly associated with the inorganic fractions of soil such as oxides of Fe, Al and clay. pH-dependent acidity at pH 8.0 was 3 to 4 times greater than that at pl/7.0. Exchangeable Al+++ was detected below pH 5.2 and AI-saturation (%) in the exchange complex varies from 2.4 to 61.3 and possess a highly significant negative correlation with soil pH. Potential acidity in soil varies from 3.4 to 13.5 cmol (p+) kg−1 of which the exchange acidity is 1 to 29.7 per cent and the rest being pl/dependent acidity. The permanent negative charge component in soil dominated over the pH - dependent one at pH 7.0 whereas, the reverse occurred at pH 8.0. More than half of the permanent charge is satisfied by H+ and Al+++ below pH 4.7 and the value decreased 10 < 2.3 per cent above pH 5.8.
Exchange acidity, pH-dependent acidity, potential acidity, permanent negative charge
