A Simple Method for Estimating Cation Exchange Capacity Accross a Wide Range of Soils.

Cation exchange capacity (CEC) is an important soil characteristic. The BaCl₂-compulsive exchange method is the recommended method for measuring the effective CEC (ECEC) of a soil at its native pH and solution ionic strength. However, this method is also a very time-consuming and expensive, and generates a hazardous waste (BaCl₂.2H₂O). As a result, soil testing laboratories do not usually measure the effective CEC, but rather estimate it from standard agronomic soil test results (summation method). The latter method is known to result in inaccurate estimates for calcareous soils. The objective of the present study was to evaluate single and double consecutive extractions with 0.01 M SrCl₂ (1:10 ratio and 5 min shaking time) for their ability to estimate ECEC. Fifty New York agricultural soils were analyzed using the BaCl₂-compulsive exchange method, and results were compared to those obtained with agronomic soil test summation methods (both Morgan and Mehlich-3) and the single and double extractions with 0.01 M SrCl₂. The soils ranged in pH from 5.1-8.4, with an organic matter level from 11-98 g kg^-1. Texture varied from sand to clay. The CEC_sum estimates based on Mehlich 3 or Morgan greatly overestimated the ECEC, mostly (but not exclusively) due to dissolution of calcium carbonate. The single extraction with 0.01 M SrCl₂ correlated well with the compulsive exchange method across all soils (slope=1.04, r² = 0.85, n=50). This method resulted in more accurate estimates of cation saturation ratios as well. A double extraction did not add to the accuracy of the prediction. We conclude a single 0.01 M SrCl₂ extraction is a simple and inexpensive method of estimating ECEC and nutrient saturation levels.