Nature of Acidity and Exchange Chemistry of Some Laterite Soils of Orissa

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.