Soil cation exchange capacity: A new method for soil science laboratories

Abstract Determining cation exchange capacity (CEC) is a foundational procedure in soil science education. Traditional introductory soil science CEC laboratory methods, both qualitative and quantitative, vary in complexity, resource requirements, and time constraints. Qualitative methods often rely on visual indicators such as cloudiness in solutions or the interaction with organic dyes, while quantitative methods, including titration endpoints and cation replacement, and may require precise analytical instrumentation. The objective of this study was to develop a time‐efficient, quantitative CEC determination method that aligns with the constraints of a 2‐h soil science laboratory. The electrical conductivity (EC) probe method proposed here was tested using soils from the North American Proficiency Testing program. Solutions of 0.05 M Ca‐acetate and 0.05 M Na‐oxalate produced a stronger correlation with CEC values ( r 2 = 0.88) than the comparison between direct and summation methods ( r 2 = 0.74). Also, the influence of soluble salts within soil samples did not interfere with the EC method. This method allows for quantitative determination of soil CEC with minimal investment, and provides reliable results for instructors and students.