National Bureau of Soil Survey and Land Use Planning, Regional Centre, Jorhat, Assam, 785013.
Present addresses: * National Bureau of Soil Survey and Land Use Planning, Shakar Nagar, Amravati Road, Nagpur, Maharashtra, 440 010.
Some chemical and electrochemical properties of six acid soils of Assam representing Alfisols, Inceptisols and Ultisols were studied. Measurement of CEC by three different methods was compared; the CEC by sum of cations and NH4OAc methods gave much higher values than effective CEC. Total potential acidity constituted 34 to 88 per cent of the total exchange capacity (extractable acidity + cations). Acidity due to variable charge (pH dependent) contributed 86 to 95 per cent of total acidity while exchange acidity contributed 5 to 14 per cent only. The variable charge characteristics were positively related with free oxides (r = 0.66) and clay content (r = 0.74) of the soils. The zero point charge (ZPC) varied from 2.4 to 3.2 while surface potential varied between -82.6 and -206.5 mV. In all the soils, the permanent charge was negative, indicating thereby that the soils though leached are not extremely weathered. The clay minerals in association with free sesquioxides and organic matter contributed towards the development ofvariable charge.
Acid soils, cation exchange capacity, potential acidity, variable charge, zero point charge
