A Simple Method for Estimating Effective Cation Exchange Capacity, Cation Saturation Ratios, and Sulfur Across a Wide Range of Soils

Cation exchange capacity (CEC) and soil S supply potential are important soil characteristics. The BaCl2-MgSO4 compulsive exchange (CECCE) method is recommended for measuring effective CEC (ECEC) of both calcareous and acidic soils. However, to reduce costs, soil testing laboratories typically report CEC estimated from agronomic soil test data (summation method; CECsum), a method that overestimates the ECEC of calcareous soils. Recently, guidance for sulfur (S) management of alfalfa (Medicago sativa L.) was derived based on a single, 30-min, 0.01-M CaCl2 soil extraction with a 1:5 (wt:vol) soil-to-solution ratio. We tested the hypothesis that a single, 5-min, 0.01-M SrCl2 soil extraction with a 1:10 (wt:vol) soil-to-solution ratio can be used to accurately estimate both ECEC and available S across a variety of soil types. Fifty New York agricultural soils (soil pH from 5.1 to 8.4) were analyzed for CECCE and cations extracted with Morgan, Mehlich 3, 1 M NH4OAc, 1 M NH4Cl, and 0.01 M SrCl2 (single and double extractions). The CECsum based on Mehlich 3, Morgan, 1 M NH4OAc, and 1 M NH4Cl extraction solutions greatly overestimated ECEC as measured by CECCE, whereas the CECsum based on a single extraction with 0.01 M SrCl2 correlated well with CECCE across all soils (slope, 1.0451; R-2 = 0.8538). Extractable S in the 5-min 0.01-M SrCl2 solution correlated well with results of the 30-min 0.01-M CaCl2 extraction (slope, 0.9685; R-2 = 0.9976). We conclude that a single 5-min 0.01-M SrCl2 extraction with 1:10 soil-to-solution ratio is a simple, rapid, and inexpensive method of estimating ECEC and plant-available S.