Use of an Ammonia Electrode for Determination of Cation Exchange Capacity in Soil Studies 1

Cation exchange capacity (CEC) was determined with an ammonia electrode on 37 horizon samples from four soil profiles. The profiles selected to test this procedure had a wide range of physical and chemical properties: (i) 19.0 to 56.7% < 2µm clay, (ii) 0.1 to 7.4% organic carbon, and (iii) 13.7 to 45.7 meq/100 g CEC. The procedure was a modification of other techniques. Centrifugation was employed for removal of exchangeable cations and ammonium salts. The CEC values obtained with the ammonia electrode agreed closely with values obtained by direct distillation for adsorbed ammonia. The differences in CEC values were not related to changes of the content of < 2 µm clay or organic carbon. The method was simple and rapid and suitable for soil studies. Using the proposed method a single operator could carry out the analysis of 16 or more samples in a normal working day.