7.Charge Characteristics and Nitrate Retention By Two Andepts from South-Central Chile

Soil Science Society of America Journal

W. Espinoza, R. G. Gast, R. S. Adams Jr.

Charge characteristics of two Andepts, or volcanic-ash-derived soils, from south-central Chile were studied using a combination of nitrate retention, pH dependent cation exchange capacity and pH titration curves. Nitrate retention was determined by washing the soil with KNO3 solutions having the appropriate concentration and pH and determining the amount of nitrate adsorbed. Net surface charge was determined from potentiometric titration curves conducted using a batch technique.

Results show that both soils have a complex mixture of pH dependent and permanent charge surfaces. The maximum pH dependent charge is in the range of 15 to 20 meq/100g at either very low or very high pH and high electrolyte concentration. The permanent negative charge is in the range of 45 meq/100g and is apparently the result of ion substitutions and lattice vacancies in X-ray amorphous oxides and hydrous oxides rather than 2:1 type clay minerals.