Contributions of Clay and Organic Matter to the Cation Exchange Capacity of Maryland Soils

Abstract Fifty‐seven profiles representing 19 soil series from the three physiographic regions of Maryland were described and sampled. The relative contributions of clay and organic matter to total cation‐exchange capacity (CEC) of various horizons were measured using multiple regression analysis. The independent variables were clay and organic matter, with the dependent variable being CEC by sum of cations. The average exchange capacities of organic matter and clay from Ap horizons were calculated to be 295 and 41 meq/100g, respectively. Standard partial regression coefficients indicated that organic matter was slightly more important than clay in predicting the CEC of surface horizons. Soils of the Coastal Plain region had higher correlations between variables than Piedmont or Appalachian soils. In fact, only the Coastal Plain soils exhibited significant correlations between clay and CEC for B and C horizons. Correlation coefficients of clay and organic matter with CEC in the Coastal Plain Ap horizons were 0.90 and 0.76, respectively, and 88% of the variation in CEC could be attributed to these components.