PRINCIPLE

The cation exchange capacity (CEC) of an acid soil can be determined by adding the milliequivalents of the determined bases (Ca, Mg, K, and Na where applicable) to the milliequivalents of exchangeable hydrogen, expressed as milliequivalents per 100 grams of soil. For most soils, the neutral normal ammonium acetate extraction procedure will give a reasonably good estimate of the soil's CEC. If a more accurate determination of a soil's CEC is desired, the procedures given in the reference can be used.

CALCULATIONS

To calculate the estimated cation exchange capacity, perform the following calculations:

lbs. K/A ÷ 780	= meq K/100 grams
lbs. Ca/A ÷ 400	= meq Ca/100 grams
lbs. Mg/A ÷ 240	= meq Mg/100 grams
lbs. Na/A ÷ 460	= meq Na/100 grams	For some soils, the failure to include Na will give slightly low results.
Exchangeable H	= meq H/100 grams	Exchangeable Hydrogen: meq H/100 g = (8.00 - buffer pH) x 8. See the Adams-Evans buffer method for Lime Requirement - Exchangeable Hydrogen for details of the procedure.
Total CEC	= meq/100 grams

REFERENCE METHOD FOR CEC DETERMINATION

1. Hesse, P.R., 1972, A Textbook of Soil Chemical Analysis, Chemical Publishing Co., N.Y., pp 91-105.
2. Jackson, M.L., 1958, Soil Chemical Analysis, Prentice-Hall, Inc., Englewood, N.J., pp 59-67.