Cation‐Exchange Capacity of Acid Soils Using Aluminum Chloride and Barium Chloride‐Triethanolamine

Base saturation is such an important criterion for classifying soils in the U.S. Soil Taxonomy that a procedure has been developed for scantily equipped field laboratories. Exchange acidity and cation‐exchange capacity (CEC) are determined in sequence with the same samples. The procedure involves (i) displacement of exchangeable hydrogen and Al with BaCl 2 ‐triethanolamine solution and back‐titration with HCl to determine the exchange acidity, (ii) saturation with Al from AlCl 3 solution, (iii) removal of excess Al with water, (iv) displacement of Al with BaCl 2 ‐triethanolamine solution and back‐titration with HCl to determine the exchange capacity, and (v) estimation of basic cations by the difference between the CEC and the exchange acidity. This is an extension of a well‐established procedure for determining exchange acidity. The CEC results compare closely with the sums of cations for acid subsoils, but are low for Al horizons with much organic matter.