15E3 Exchangeable bases, CEC and AEC by compulsive exchange, adjusted for soluble Na⁺

This method is identical to 15E1 except that a calculation, based on the amount of soluble Cl^– present, is used to adjust for the apparent level of exchangeable Na⁺ present in the soil. This approximate correction for soluble Na⁺ is an alternative to chemical pre-treatment when EC (1:5, soil/water) exceeds 0.3 dS/m and NaCl is the dominant soluble salt.

Procedure

Proceed as described in Method 15E1.

Calculation and Reporting

Convert mg Cl^–/kg (from Method 5A1 or 5A2) to cmol_cCl/kg by dividing by 354.5. On the assumption that all soluble Cl^– is associated with Na⁺, calculate the corrected value as follows:

Report exchangeable Ca²⁺, Mg²⁺, and K⁺ (cmol_c/kg) as determined from Method 15E1, and exchangeable Na⁺ as corrected above (cmol_c/kg). Express results on an oven-dry basis. Use the air-dry moisture to oven-dry moisture ratio to convert to an oven-dry concentration. Refer to Method 2A1 for guidance with regard to this soil moisture calculation.

Report CEC_B and AEC as described for Method 15E1.